Mizuho discloses 8% SilverBox Corp IV stake in SBXD shares

Rhea-AI Filing Summary

Mizuho Financial Group, Inc., a Japan-based parent holding company, reported beneficial ownership of 1,645,673 SilverBox Corp IV common shares, representing 8.0% of the class as of the event date 12/31/2025. Mizuho has sole power to vote and dispose of these shares, with no shared voting or dispositive power.

The filing notes that Mizuho Financial Group, Mizuho Bank, Ltd. and Mizuho Americas LLC may be deemed indirect beneficial owners of equity securities directly held by their wholly owned subsidiary, Mizuho Securities USA LLC. The securities are stated to be acquired and held in the ordinary course of business and not for changing or influencing control of SilverBox Corp IV.

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

SilverBox Corp IV

(Name of Issuer)

Common Shares

(Title of Class of Securities)

G81354105

(CUSIP Number)

12/31/2025

(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)

SCHEDULE 13G

CUSIP No. G81354105

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 1,645,673.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 1,645,673.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

1,645,673.00

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: SilverBox Corp IV
(b)	Address of issuer's principal executive offices: 8701 BEE CAVE ROAD, EAST BUILDING, SUITE 310, AUSTIN, TX 78746
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.: G81354105
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: 1,645,673
(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: 1,645,673
	(ii) Shared power to vote or to direct the vote: 0
	(iii) Sole power to dispose or to direct the disposition of: 1,645,673
	(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:	02/12/2026

FAQ

What percentage of SilverBox Corp IV (SBXD) does Mizuho Financial Group own?

Mizuho Financial Group reports beneficial ownership of 8.0% of SilverBox Corp IV’s common shares. This stake reflects 1,645,673 shares and gives Mizuho sole voting and dispositive power over that block, according to the Schedule 13G filing.

How many SilverBox Corp IV (SBXD) shares does Mizuho Financial Group hold?

Mizuho Financial Group reports beneficial ownership of 1,645,673 SilverBox Corp IV common shares. The filing states Mizuho has sole power to vote and dispose of all these shares, with no shared voting or dispositive authority indicated in the ownership table.

Is Mizuho Financial Group’s stake in SBXD considered passive or for control purposes?

The filing certifies the securities were acquired and are held in the ordinary course of business, not to change or influence control of SilverBox Corp IV. It also states they are not held in connection with any transaction intended to affect control, aside from certain nomination-related activities.

Through which entity does Mizuho Financial Group hold SilverBox Corp IV shares?

Mizuho Financial Group, Mizuho Bank, Ltd. and Mizuho Americas LLC may be deemed indirect beneficial owners of shares directly held by Mizuho Securities USA LLC, their wholly owned subsidiary. The Schedule 13G notes this indirect beneficial ownership structure in the type of reporting person comments.

What voting power does Mizuho have over its SBXD shares?

Mizuho reports 1,645,673 shares with sole voting power and 0 shares with shared voting power. It also lists the same number with sole dispositive power and none with shared dispositive power, indicating full control over voting and disposition of the reported stake.

When was Mizuho’s 8% ownership position in SBXD measured?

The ownership position is reported as of the event date 12/31/2025. On that date, Mizuho Financial Group’s beneficial stake in SilverBox Corp IV’s common shares was disclosed at 1,645,673 shares, representing 8.0% of the outstanding class in the Schedule 13G.