Rainier Acquisition Corp

As filed with the United States Securities and Exchange Commission on August 6, 2026.

No. 333-

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM****S-1

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

(Exact name of registrant as specified in its charter)

1 Penn Plaza, 48th floor

New York, NY 10119

Tel.: (646) 465-9000

(Address, including zip code, and telephone number, including area code, of registrant’s principal executive offices)

Gbola Amusa, M.D., CFA

Chief Executive Officer

1 Penn Plaza, 48th floor

New York, NY 10119

Tel.: (646) 465-9000

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies:

**Approximate date of commencement of proposed sale to the public:**As soon as practicable after the effective date of this registration statement.

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933 check the following box:☐

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.☐

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.☐

If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act.☐

The Registrant hereby amends this Registration Statement on such date or dates as may be necessary to delay its effective date until the Registrant shall file a further amendment which specifically states that this Registration Statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933, as amended, or until the Registration Statement shall become effective on such date as the Securities and Exchange Commission, acting pursuant to said Section 8(a), may determine.

The information in this preliminary prospectus is not complete and may be changed. We may not sell these securities until the registration statement filed with the Securities and Exchange Commission is effective. This preliminary prospectus is not an offer to sell these securities and it is not soliciting an offer to buy these securities in any jurisdiction where the offer or sale is not permitted.

SUBJECT TO COMPLETION, DATED AUGUST 6, 2026

PRELIMINARY PROSPECTUS

$75,000,000

7,500,000 Units

Rainier Acquisition Corporation, a Cayman Islands exempted company, is a blank check company for the purpose of effecting a merger, amalgamation, share exchange, asset acquisition, share purchase, reorganization or similar business combination with one or more businesses or entities, which we refer to as our initial business combination. We have not selected any business combination target and we have not, nor has anyone on our behalf, initiated any substantive discussions, directly or indirectly, with any business combination target. We will not be limited to a particular industry or geographic region in our identification and acquisition of a target company.

This is an initial public offering of our securities. Each unit has an offering price of $10.00 and consists of one Class A ordinary share and one-quarter of one redeemable warrant. Each whole warrant entitles the holder thereof to purchase one Class A ordinary share at a price of $11.50 per share, subject to adjustment, terms and limitations as described herein. The underwriters have a 45-day option from the date of this prospectus to purchase up to 1,125,000 additional units to cover over-allotments, if any.

We will provide our public shareholders with theopportunity to redeem all or a portion of their Class A ordinary shares upon the completion of our initial business combination, subject to the limitations as described herein. If we have not consummated an initial business combination within 24 months from the closing of this offering, or such earlier liquidation date as our board of directors may approve, which we refer to as the “completion window,” we will redeem 100% of the public shares for cash, subject to applicable law and certain conditions as described herein.

Currently, there is no public market for our securities. We intend to apply to have our units listed on the Nasdaq Capital Market (“Nasdaq”), under the symbol “RNAQU.” We expect that the Class A ordinary shares and warrants comprising the units will begin separate trading on Nasdaq under the symbols “RNAQ” and “RNAQW,” respectively, on the 52nd day following the date of this prospectus unless the underwriters permit earlier separate trading and we have satisfied certain conditions.

Our sponsor, Ravenna 7 LLC, has agreed to purchase an aggregate of 194,375 private placement units (or up to 200,000 private placement units if the underwriters’ over-allotment option is exercised in full), at a price of $10.00 per unit, for an aggregate purchase price of $1,943,750 (or up to $2,000,000 if the underwriters’ over-allotment option is exercised in full) in a private placement that will close simultaneously with the closing of this offering. We refer to these units throughout this prospectus as the private placement units. Each private placement unit is identical to the public units except that the private warrants contained therein will be non-redeemable and may be exercised on a cashless basis, but in each case only if they are held by the sponsor, subject to certain limited exceptions, as described in this prospectus. None of the private placement warrants will be redeemable by us. Each private placement share included in each private placement unit will not have any redemption rights or be entitled to liquidating distributions from the trust account if we fail to consummate an initial business combination.

Further, our sponsor currently owns 2,156,250 of our Class B ordinary shares (up to 281,250 of which are subject to forfeiture), which will automatically convert into Class A ordinary shares at the time of our initial business combination or earlier at the option of the holder on a one-for-one basis (such Class A ordinary shares issued upon conversion will not have any redemption rights or be entitled to liquidating distributions from the trust account if we fail to consummate an initial business combination), subject to adjustment as described herein. Prior to the completion of our initial business combination, only holders of our Class B ordinary shares will be entitled to vote on the appointment or removal of directors or in a vote to transfer the company by way of continuation to a jurisdiction outside the Cayman Islands (including any special resolution required to amend the constitutional documents of the company or to adopt new constitutional documents of the company, in each case, as a result of the company approving a transfer by way of continuation in a jurisdiction outside the Cayman Islands). The founder shares held by our sponsor were purchased for $25,000, or approximately $0.01159 per share (after giving effect to the share adjustment), which, as further described in this prospectus, may result in material dilution to public holders when converted into Class A ordinary shares or if the anti-dilution provision of the founder shares results in the issuance of Class A ordinary shares on a greater than one-to-one basis (for more information on dilution, also see the section entitled “Dilution” in this prospectus). If we increase or decrease the size of this offering, we will effect a share capitalization, a share surrender or redemption or other appropriate mechanism, as applicable, with respect to our Class B ordinary shares immediately prior to the consummation of this offering in such amount as to maintain the number of founder shares, on an as-converted basis, at 20% of our issued and outstanding ordinary shares upon the consummation of this offering. As further described under “The Offering—Conflicts of Interest” and “Proposed Business—Sponsor Information*,” we expect to make certain payments and reimbursements, or pay certain fees, to our sponsor, officers or directors, or our or their affiliates. Our sponsor, officers and directors and their affiliates may also, but are not obligated to, enter into certain arrangements with us to finance transaction costs in connection with an initial business combination, including up to $1,500,000 of loans convertible into private placement units at a price of $10.00 per private placement unit at the option of the lender. As more fully discussed in the section of this prospectus entitled “Management—Conflicts of Interest,” our officers and directors currently have certain relevant fiduciary duties or contractual obligations that may take priority over their duties to us and there may be a conflict of interest in our director’s and officer’s determination as to how much time to devote to our affairs and to which entity a particular business opportunity is presented. We may also decide to acquire one or more businesses affiliated with our sponsor or our executive officers or directors, or our directors, officers, sponsor and their affiliates may sponsor or become affiliated with entities that have similar activities to ours. Further, our officers and directors have indirect economic interests in us and/or our sponsor and a conflict of interest may arise in determining whether a particular business combination target is appropriate for our initial business combination since our sponsor, executive officers and directors may lose their entire investment in us if an initial business combination is not completed. As a result, there may be actual or potential material conflicts of interest between our sponsor and its affiliates on the one hand, and purchasers in this offering on the other hand. See “The Offering—Founder shares,” “The Offering—Transfer restrictions on founder shares,” “The Offering—Appointment of directors; Voting rights,”The Offering—Private placement units,” “The Offering—Transfer restrictions on private placement units,” “The Offering—Conflicts of Interest,” “Risk Factors—Risks Relating to our Search for, Consummation of, or Inability to Consummate, a Business Combination and Post-Business Combination Risks—The ability of our public shareholders to redeem their shares for cash may make our financial condition unattractive to potential business combination targets, which may make it difficult for us to enter into a business combination with a target,” “Risk Factors—Risks Relating to our Search for, Consummation of, or Inability to Consummate, a Business Combination and Post-Business Combination Risks—The ability of our public shareholders to exercise redemption rights with respect to a large number of our shares may not allow us to complete the most desirable business combination or optimize our capital structure,” “Risk Factors—Risks Relating to our Sponsor and Management Team,” “Use of Proceeds,” “Dilution,” “Proposed Business—Sponsor Information,” “Principal Shareholders,” and “Certain Relationships and Related Party Transactions.*”

Because our sponsor acquired the founder shares at a nominal price, our public shareholders will incur an immediate and substantial dilution upon the closing of this offering, assuming no value is ascribed to the public warrants included in the units. Further, the Class A ordinary shares issuable in connection with the conversion of the founder shares may result in material dilution to our public shareholders due to the anti-dilution rights of our founder shares that may result in an issuance of Class A ordinary shares on a greater than one-to-one basis upon conversion. See “Risk Factors—Risks Relating to Our Securities—The nominal purchase price paid by our sponsor for the founder shares may result in significant dilution to the implied value of your public shares upon the consummation of our initial business combination, and our sponsor is likely to make a substantial profit on its investment in us in the event we consummate an initial business combination, even if the business combination causes the trading price of our ordinary shares to materially decline.”

The following table illustrates the difference between the public offering price per unit and our net tangible book value per share (“NTBV”), as adjusted to give effect to this offering and assuming the redemption of our public shares included in the public units offered hereby at varying levels in the scenarios in which the over-allotment option is not exercised and exercised in full. See “Dilution” for more information.

Members of our sponsor are associated persons of Chardan Capital Markets LLC (“Chardan”), the representative of the underwriters in this offering. These parties have an economic interest in 100% of our founder shares (2,156,250 founder shares, up to 281,250 of which are subject to forfeiture if the underwriters’ over-allotment option is not exercised in full) held by our sponsor and will have an economic interest in 100% of our private placement units (194,375 private placement units or 200,000 private placement units if the underwriters’ over-allotment option is exercised in full) that will be purchased by our sponsor in a private placement that will close simultaneously with the closing of this offering. Jonas Grossman, a member of our board of directors and an associated person of Chardan, is the sole managing member of our sponsor and controls the exercise of voting and investment discretion over the securities held by our sponsor. In addition, we will pay Chardan the upfront underwriting compensation upon the completion of this offering and the deferred underwriting fee upon the consummation of our initial business combination in an aggregate amount equal to 3.5% of the gross proceeds from this offering. Chardan will also have a right of first refusal to participate as a co-lead placement agent, bookrunner or arranger on future financings. As a result, Chardan is deemed to have a “conflict of interest” within the meaning of FINRA Rule 5121. Accordingly, this offering is being made in compliance with the applicable requirements of FINRA Rule 5121. Rule 5121 requires that a “qualified independent underwriter,” as defined in Rule 5121, participate in the preparation of the registration statement and prospectus and exercise the usual standards of due diligence with respect thereto. B. Riley Securities, Inc. (“B. Riley”) has agreed to act as a “qualified independent underwriter” for this offering. B. Riley will receive a fee for acting as a “qualified independent underwriter.” We have agreed to indemnify B. Riley against certain liabilities incurred in connection with acting as a “qualified independent underwriter,” including liabilities under the Securities Act. In addition, no underwriter with a conflict of interest will confirm sales to any account over which it exercises discretionary authority without the specific prior written approval of the account holder. See “Underwriting (Conflicts of Interest).”

We are an “emerging growth company” and a “smaller reporting company” under applicable federal securities laws and will be subject to reduced public company reporting requirements.

Investing in our securities involves a high degree of risk.See“Risk Factors**” beginning on page32 for a discussion of information that should be considered in connection with an investment in our securities.** Investors will not be entitled to protections normally afforded to investors in Rule 419 blank check offerings.

Neither the Securities and Exchange Commission (the “SEC”) nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

Of the proceeds we receive from this offering and the sale of the private placement units described in this prospectus, $75,000,000, or $86,250,000 if the underwriters’ over-allotment option is exercised in full ($10.00 per unit in either case), will be deposited into a U.S.-based trust account with Continental Stock Transfer & Trust Company acting as trustee.

The underwriters are offering the units for sale on a firm commitment basis. The underwriters expect to deliver the units to the purchasers on or about , 2026.

Sole Book-Running Manager

Chardan

The date of this prospectus is , 2026

We are responsible for the information contained in this prospectus. We have not authorized anyone to provide you with different information, and neither we nor the underwriters take any responsibility for any other information others may give to you. We are not, and the underwriters are not, making an offer to sell securities in any jurisdiction where the offer or sale is not permitted. You should not assume that the information contained in this prospectus is accurate as of any date other than the date on the front of this prospectus.