MFG Mizuho Financial Group Inc

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 6-K

REPORT OF FOREIGN PRIVATE ISSUER

PURSUANT TO RULE 13a-16 OR 15d-16

UNDER THE SECURITIES EXCHANGE ACT OF 1934

For the month of February 2024

Commission File Number 001-33098

Mizuho Financial Group, Inc.

(Translation of registrant’s name into English)

1-5-5 Otemachi

Chiyoda-ku, Tokyo 100-8176

Japan

(Address of principal executive office)

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F. Form 20-F ☒ Form 40-F ☐

Indicate by check mark whether the registrant by furnishing the information contained in this Form is also thereby furnishing the information to the Commission pursuant to Rule 12g3-2(b) under the Securities Exchange Act of 1934. Yes ☐ No ☒

If “Yes” is marked, indicate below the file number assigned to the registrant in connection with Rule 12g3-2(b): 82-    .

The information and exhibits set forth in this Form 6-K shall be deemed to be incorporated by reference into the prospectus forming a part of Mizuho Financial Group, Inc.’s Registration Statement on Form F-3 (File No. 333-266555) and to be a part of such prospectus from the date on which this report is furnished, to the extent not superseded by documents or reports subsequently filed or furnished.

EXHIBIT INDEX

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

Exhibit 5.1

February 26, 2024

Mizuho Financial Group, Inc.

1-5-5, Otemachi,

Chiyoda-ku, Tokyo 100-8176,

Japan

MIZUHO FINANCIAL GROUP, INC.

Registration Statement on Form F-3

Ladies and Gentlemen:

In connection with the registration statement (the “Registration Statement”) on Form F-3 (File No. 333-266555) relating to debt securities of Mizuho Financial Group, Inc. (the “Issuer”), and the offering outside Japan by the Issuer of $750,000,000 aggregate principal amount of its 5.376% senior callable fixed-to-fixed reset rate notes due 2030 and $750,000,000 aggregate principal amount of its 5.579% senior callable fixed-to-fixed reset rate notes due 2035 (collectively, the “Notes”) pursuant to the underwriting agreement in respect of the Notes, dated February 20, 2024, between the Issuer and the Underwriters named therein (the “Underwriting Agreement”), we have acted as Japanese legal counsel to the Issuer and have been requested to provide our opinion to be filed as an exhibit to the Registration Statement.

For the purposes of giving this opinion, we have examined, among other things, the following documents:

We have also examined such certificates and corporate documents of the Issuer and such other matters, documents and records, and considered such questions of the laws of Japan, as we have deemed necessary or appropriate for the purpose of rendering the opinion hereinafter set forth.

Having examined the above documents and having regard to the laws of Japan which we deem relevant, and subject to the assumptions and qualifications specified herein, we are of the opinion that:

The Notes, when payment for the Notes has been duly made in full in accordance with the Underwriting Agreement, and when the Global Certificates have been duly signed on behalf of the Issuer by a Representative Executive Officer of the Issuer or persons named in the Power of Attorney, duly authenticated and delivered in accordance with the terms of the Underwriting Agreement, the Indenture and the Notes, and assuming that the Notes will constitute valid and legally binding obligations of the Issuer enforceable in accordance with their terms under their governing law, to which they are subject and as to which we render no opinion, will constitute valid and legally binding obligations of the Issuer enforceable in accordance with their terms.

We have assumed, for the purpose of rendering this opinion, that (i) all signatures or seal impressions on any documents we reviewed are true and genuine; (ii) all documents submitted to us as originals are authentic and complete; (iii) all documents submitted to us as copies are complete and conform to the originals thereof that are authentic and complete; (iv) all documents submitted to us as forms are executed in such forms; (v) statements included, expressly or impliedly, in the documents, record and certificate of the Issuer or public officials are true and conform to the relevant facts thereof; (vi) all natural person-signatories who have executed or delivered the Underwriting Agreement, the Indenture and other documents related thereto on behalf of the relevant parties thereto have and had at the relevant times the sufficient and competent legal capacity to take such actions; (vii) each party (other than the Issuer) to each of the Underwriting Agreement, the Indenture and other relevant documents is an entity duly organized, validly existing and, where applicable, in good standing under the laws of the jurisdiction of its organization, and has full and complete power and authority (corporate or otherwise) to execute and deliver, and to perform its obligations under, such document; (viii) each of the Underwriting Agreement, the Indenture and other relevant documents is within the capacity and powers of and has been duly authorized by all the parties thereto (other than the Issuer); (ix) each of the Underwriting Agreement, the Indenture and other relevant documents has been duly executed and delivered by all the parties thereto (other than the Issuer); (x) nothing in the applicable law of any jurisdiction other than Japan would conflict with, or preclude the performance, legality, validity, effectiveness or enforcement of, the Notes and the Underwriting Agreement, the Indenture and other relevant documents; and (xi) the Underwriting Agreement, the Indenture and other relevant documents are legal, valid and binding on the parties thereto and enforceable in accordance with their respective terms under their respective governing laws (other than the laws of Japan). We have not independently verified any of the matters referred to in (i) through (xi) above.

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The foregoing opinion is based on the assumptions, qualified by and subject to the limitations, set forth below:

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We hereby consent to the use of this opinion as an exhibit to a current report on Form 6-K to be filed by the Issuer on the date hereof incorporated by reference into the Registration Statement and to the use of our name under the captions “Legal Matters” and “Enforcement of Civil Liabilities” contained in the Registration Statement. In giving this consent, we do not thereby admit that we come within the category of persons whose consent is required by the U.S. Securities Act of 1933, as amended, or by the rules and regulations under it.

Very truly yours,

/s/ NAGASHIMA OHNO & TSUNEMATSU

(IO/MKK)

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Exhibit 5.2

February 26, 2024

Mizuho Financial Group, Inc.

1-5-5 Otemachi, Chiyoda-ku

Tokyo 100-8176, Japan

Ladies and Gentlemen:

We have acted as United States counsel to Mizuho Financial Group, Inc., a joint stock company incorporated with limited liability under the law of Japan (the “Company”), in connection with the Registration Statement on Form F-3 (File No. 333-266555) (the “Registration Statement”) filed by the Company with the U.S. Securities and Exchange Commission (the “Commission”) under the U.S. Securities Act of 1933, as amended, relating to the issuance by the Company of U.S.$750,000,000 aggregate principal amount of 5.376% Senior Callable Fixed-to-Fixed Reset Rate Notes due 2030 and U.S.$750,000,000 aggregate principal amount of 5.579% Senior Callable Fixed-to-Fixed Reset Rate Notes due 2035 (collectively, the “Securities”) pursuant to the Senior Indenture, dated as of September 13, 2016 (the “Indenture”), between the Company and The Bank of New York Mellon, as trustee (the “Trustee”).

We have examined the Registration Statement, the Indenture, the Officer’s Certificate, dated as of February 26, 2024, delivered pursuant to the Indenture establishing the terms of the Securities, duplicates of the global notes representing the Securities, and the underwriting agreement, dated February 20, 2024 (the “Underwriting Agreement”), between the Company and the several underwriters named in Schedule A thereto. In addition, we have examined, and have relied as to matters of fact upon, originals, or duplicates or certified or conformed copies, of such records, agreements, documents and other instruments and such certificates or comparable documents of public officials and of officers and representatives of the Company and have made such other investigations as we have deemed relevant and necessary in connection with the opinions hereinafter set forth.

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In rendering the opinion set forth below, we have assumed the genuineness of all signatures, the legal capacity of natural persons, the authenticity of all documents submitted to us as originals, the conformity to original documents of all documents submitted to us as duplicates or certified or conformed copies and the authenticity of the originals of such latter documents. We have also assumed that the Indenture is the valid and legally binding obligation of the Trustee.

In rendering the opinion set forth below, we have assumed further that (1) the Company has been duly incorporated and is validly existing under the law of Japan and has duly authorized, executed, issued and delivered the Indenture, the Securities and the Underwriting Agreement, as applicable, in accordance with its Articles of Incorporation, its Regulations of the Board of Directors and the law of Japan, (2) the execution, issuance, delivery and performance by the Company of the Indenture, the Securities and the Underwriting Agreement, as applicable, do not constitute a breach or violation of its Articles of Incorporation or its Regulations of the Board of Directors or violate the law of Japan or any other jurisdiction (except that no such assumption is made with respect to the federal law of the United States or the law of the State of New York) and (3) the execution, issuance, delivery and performance by the Company of the Indenture, the Securities and the Underwriting Agreement, as applicable, do not constitute a breach or default under any agreement or instrument which is binding upon the Company.

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Based upon the foregoing, and subject to the qualifications, assumptions and limitations stated herein, we are of the opinion that assuming due authentication of the Securities by the Trustee, and upon payment and delivery in accordance with the provisions of the Underwriting Agreement, the Securities will constitute valid and legally binding obligations of the Company enforceable against the Company in accordance with their terms.

Our opinion set forth above is subject to (i) the effects of bankruptcy, insolvency, fraudulent conveyance, reorganization, moratorium and other similar laws relating to or affecting creditors’ rights generally, (ii) general equitable principles (whether considered in a proceeding in equity or at law), (iii) an implied covenant of good faith and fair dealing and (iv) the effects of the possible application of foreign laws or foreign governmental or judicial action affecting creditors’ rights. In addition, we express no opinion with respect to Section 4.13 of the Indenture relating to indemnification of judgment currency.

In connection with the provision of the Indenture whereby the parties submit to the jurisdiction of U.S. federal courts located in the Borough of Manhattan, The City of New York, we note the limitations of 28 U.S.C. Sections 1331 and 1332 on subject matter jurisdiction of the U.S. federal courts. In connection with the provision of the Indenture which relates to forum selection (including, without limitation, any waiver of any objection to venue or any objection that a court is an inconvenient forum), we note that under N.Y.C.P.L.R. Section 510, a New York State court may have discretion to transfer the place of trial, and under 28 U.S.C. Section 1404(a), a U.S. federal district court has discretion to transfer an action from one U.S. federal court to another. We also note that the recognition and enforcement in New York State courts or U.S. federal courts sitting in the State of New York of a foreign judgment obtained against the Company is subject to the Uniform Foreign Money—Judgments Recognition Act (53 N.Y.C.P.L.R. §5301 et seq.).

We do not express any opinion herein concerning any law other than the law of the State of New York and the federal law of the United States.

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We hereby consent to the filing of this opinion letter as Exhibit 5.2 to the Form 6-K of the Company filed with the Commission on February 26, 2024 in connection with the offer and sale of the Securities by the Company for incorporation into the Registration Statement and to the use of our name under the caption “Legal Matters” in the prospectus included in the Registration Statement.

Very truly yours,

/s/ Simpson Thacher & Bartlett LLP

SIMPSON THACHER & BARTLETT LLP