Mizuho reports 8.0% stake in Quartzsea Acquisition

Mizuho Financial Group, Inc., a parent holding company organized in Japan, reports beneficial ownership of common shares of Quartzsea Acquisition Corporation.

Rhea-AI Filing Summary

Mizuho Financial Group, Inc., a parent holding company organized in Japan, reports beneficial ownership of common shares of Quartzsea Acquisition Corporation. Mizuho reports beneficial ownership of 993,296 common shares, representing 8.0% of the class. It has sole power to vote and dispose of all 993,296 shares and no shared voting or dispositive power. The shares are directly held by Mizuho Securities USA LLC, a wholly owned subsidiary, and Mizuho Financial Group, Inc., Mizuho Bank, Ltd. and Mizuho Americas LLC may be deemed indirect beneficial owners.

Key Figures

Shares beneficially owned: 993,296 shares Ownership percentage: 8.0% Sole voting power: 993,296 shares +3 more

6 metrics

Shares beneficially owned 993,296 shares Common Shares of Quartzsea Acquisition Corporation beneficially owned by Mizuho Financial Group, Inc.

Ownership percentage 8.0% Percent of Quartzsea Acquisition Corporation common share class reported as beneficially owned

Sole voting power 993,296 shares Number of shares over which Mizuho has sole power to vote or direct the vote

Sole dispositive power 993,296 shares Number of shares over which Mizuho has sole power to dispose or direct the disposition

CUSIP G7314B104 CUSIP number for Quartzsea Acquisition Corporation common shares

Signature date 08/13/2026 Date of signature by Takahiro Katsura on behalf of Mizuho Financial Group, Inc.

Key Terms

beneficially owned, sole voting power, sole dispositive power, parent holding company, +1 more

5 terms

beneficially owned financial

"Amount beneficially owned: 993,296 (b) Percent of class: 8.0 %"

Beneficially owned describes securities or assets where a person has the economic rights and control—such as the right to receive dividends and to direct voting—even if legal title is held in another name. Think of it like having the keys and using a car that’s registered to someone else: you get the benefits and make decisions. Investors care because beneficial ownership reveals who truly controls value and voting power, affecting corporate decisions and takeover dynamics.

sole voting power financial

"Sole power to vote or to direct the vote: 993,296"

Sole voting power is the exclusive right to cast votes attached to a shareholder’s stock without needing approval from anyone else. Like holding the only remote control for a TV, it lets that holder decide corporate matters such as board members, mergers, and policy changes, making it important to investors because it concentrates control and can strongly influence a company’s strategy and the value of its shares.

sole dispositive power financial

"Sole power to dispose or to direct the disposition of: 993,296"

Sole dispositive power is the exclusive legal authority to decide what happens to a security — for example, whether to sell, transfer, or retain shares — without needing anyone else’s permission. Investors care because it signals who truly controls the economic outcome of an investment: like holding the only key to a safe, the holder can realize gains or losses and may trigger regulatory reporting, insider rules, or influence over corporate ownership.

parent holding company financial

"CUSIP No.: G7314B104 | Parent Holding Company Item 4."

indirect beneficial owners financial

"may be deemed to be indirect beneficial owners of said equity securities"

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What stake in Quartzsea Acquisition Corporation (QSEA) does Mizuho Financial Group report?

Mizuho Financial Group reports beneficial ownership of 993,296 common shares of Quartzsea Acquisition Corporation, representing 8.0% of the outstanding class. This ownership is reported with sole voting and dispositive power over all such shares.

How much voting power does Mizuho Financial Group have in QSEA?

Mizuho Financial Group reports sole voting power over 993,296 shares of Quartzsea Acquisition Corporation and no shared voting power. It also reports sole dispositive power over the same number of shares and no shared dispositive power.

Which entities are involved in Mizuho’s QSEA holdings?

The shares are directly held by Mizuho Securities USA LLC, a wholly owned subsidiary. Mizuho Financial Group, Inc., Mizuho Bank, Ltd. and Mizuho Americas LLC may be deemed indirect beneficial owners of the equity securities held by Mizuho Securities USA LLC.

What class of securities of QSEA does Mizuho Financial Group own?

Mizuho Financial Group reports beneficial ownership of Common Shares of Quartzsea Acquisition Corporation, identified by CUSIP G7314B104. The holding totals 993,296 common shares, amounting to 8.0% of that class of securities.

What is the ownership percentage reported by Mizuho Financial Group in QSEA?

Mizuho Financial Group reports that its beneficial ownership of Quartzsea Acquisition Corporation common shares represents 8.0% of the class. This percentage relates to the 993,296 common shares over which it has sole voting and dispositive power.

Who signed the beneficial ownership report for Mizuho Financial Group regarding QSEA?

The report was signed by Takahiro Katsura, identified as Managing Director, Global Corporate Function Coordination Department. The signature is dated 08/13/2026, certifying the information and certain regulatory comparability statements.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Accepted by SEC EDGAR 08/13/2026 - 06:17 AM EDT Learn about SEC filing dates

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 1)

Quartzsea Acquisition Corporation

(Name of Issuer)

Common Shares

(Title of Class of Securities)

G7314B104

(CUSIP Number)

06/30/2026

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

Rule 13d-1(b)

Rule 13d-1(c)

Rule 13d-1(d)

schemaVersion:

SCHEDULE 13G

CUSIP Number(s): G7314B104

1

Names of Reporting Persons

Mizuho Financial Group, Inc.

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

JAPAN

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 993,296.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 993,296.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

993,296.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

8.0 %

12

Type of Reporting Person (See Instructions)

FI

Comment for Type of Reporting Person: Mizuho Financial Group, Inc., Mizuho Bank, Ltd. and Mizuho Americas LLC may be deemed to be indirect beneficial owners of said equity securities directly held by Mizuho Securities USA LLC which is their wholly-owned subsidiary.

SCHEDULE 13G

Item 1.
(a)	Name of issuer: Quartzsea Acquisition Corporation
(b)	Address of issuer's principal executive offices: 1185 Avenue of the Americas, Suite 304, New York, NY 10036
Item 2.
(a)	Name of person filing: Mizuho Financial Group, Inc.
(b)	Address or principal business office or, if none, residence: 1-5-5, Otemachi, Chiyoda-ku, Tokyo, 100-8176, Japan
(c)	Citizenship: Japan
(d)	Title of class of securities: Common Shares
(e)	CUSIP No.: G7314B104
Item 3.	If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:
(a)	Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);
(b)	Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);
(c)	Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);
(d)	Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
(e)	An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);
(f)	An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
(g)	A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
(h)	A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
(i)	A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);
(j)	A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J), please specify the type of institution:
(k)	Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).
	Parent Holding Company
Item 4.	Ownership
(a)	Amount beneficially owned: 993,296
(b)	Percent of class: 8.0 %
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: 993,296
	(ii) Shared power to vote or to direct the vote: 0
	(iii) Sole power to dispose or to direct the disposition of: 993,296
	(iv) Shared power to dispose or to direct the disposition of: 0
Item 5.	Ownership of 5 Percent or Less of a Class.
	Not Applicable
Item 6.	Ownership of more than 5 Percent on Behalf of Another Person.
	Not Applicable
Item 7.	Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.
	If a parent holding company has filed this schedule, pursuant to Rule 13d-1(b)(ii)(G), so indicate under Item 3(g) and attach an exhibit stating the identity and the Item 3 classification of the relevant subsidiary. If a parent holding company has filed this schedule pursuant to Rule 13d-1(c) or Rule 13d-1(d), attach an exhibit stating the identification of the relevant subsidiary. See Exhibit A
Item 8.	Identification and Classification of Members of the Group.
	Not Applicable
Item 9.	Notice of Dissolution of Group.
	Not Applicable

Item 10.

Certifications:

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under § 240.14a-11. By signing below I certify that, to the best of my knowledge and belief, the foreign regulatory scheme applicable to Parent Holding Company is substantially comparable to the regulatory scheme applicable to the functionally equivalent U.S. institution(s). I also undertake to furnish to the Commission staff, upon request, information that would otherwise be disclosed in a Schedule 13D.

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Mizuho Financial Group, Inc.

Signature:	/s/ Takahiro Katsura
Name/Title:	Takahiro Katsura, Managing Director, Global Corporate Function Coordination Department
Date:	08/13/2026