[SCHEDULE 13D/A] C3is Inc. SEC Filing

Rhea-AI Filing Summary

C3is Inc. reporting persons updated their Schedule 13D to reflect dilution from recent share issuances and warrant exercises that reduced their stakes below prior thresholds. Together the three reporting parties hold 100,577 shares, representing 3.7% of the outstanding common stock. The largest holder in the group, Arethusa Properties LTD, beneficially owns 72,331 shares (2.7%), while Flawless Management Inc. reports beneficial ownership of 4 shares (0.01%). The filing notes that share counts were adjusted for multiple reverse stock splits and that the reporting persons continue to hold their positions for investment purposes; Harry N. Vafias serves as Non-Executive Chairman and may engage with management and the board on strategic matters.

Positive

• Continued governance role by Harry N. Vafias as Non-Executive Chairman despite dilution
• Joint Filing Agreement among the three reporting persons clarifies coordinated ownership and intentions

Negative

• Ownership diluted below the 5% threshold, now 3.7%, reducing certain reporting status
• Material dilution resulted from share issuances and warrant exercises, lowering influence measured by percentage ownership

Insights

Securities Ownership Analyst

Holdings fell below the 5% reporting threshold due to dilution.

The group aggregate ownership is 100,577 shares or 3.7%, reduced after the issuer issued shares and warrants were exercised. This change removes the reporting persons from the >5% category described in the statement.

Key dependencies include future issuances or warrant exercises that could further dilute percentages and any open-market transactions by the reporting persons; monitor outstanding warrants and supplemental prospectus details for potential reversals of dilution over the near term.

Corporate Governance Advisor

Active insider role preserved despite lower ownership stake.

Harry N. Vafias remains Non-Executive Chairman and is part of a joint filing with two entities, indicating continued governance involvement even though the group's ownership is now below 5%. The filing expressly reserves the right to consider a range of corporate actions.

Watch for any formal proposals or changes in board composition tied to these discussions; governance influence may persist absent a large equity stake, so near-term board communications and meeting outcomes are relevant.

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 4)

C3IS INC.

(Name of Issuer)

Common Stock, par value $0.01 per share

(Title of Class of Securities)

Y18284169

(CUSIP Number)

Harry N. Vafias
c/o C3is Inc., 331 Kifissias Avenue Kifissia
Athens, J3, 14561
011 30 210 625 0001

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

10/09/2025

(Date of Event Which Requires Filing of This Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box.

The information required on the remainder of this cover page shall not be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

SCHEDULE 13D

CUSIP No. Y18284169

1

Name of reporting person

Flawless Management Inc.

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

OO

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

MARSHALL ISLANDS

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 4.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 4.00

11

Aggregate amount beneficially owned by each reporting person

4.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

0.01 %

14

Type of Reporting Person (See Instructions)

CO

SCHEDULE 13D

CUSIP No. Y18284169

1

Name of reporting person

Arethusa Properties LTD

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

OO

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

VIRGIN ISLANDS, BRITISH

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 72,331.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 72,331.00

11

Aggregate amount beneficially owned by each reporting person

72,331.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

2.7 %

14

Type of Reporting Person (See Instructions)

CO

SCHEDULE 13D

CUSIP No. Y18284169

1

Name of reporting person

Harry N. Vafias

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

OO

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

GREECE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 28,242.00
8	Shared Voting Power 72,335.00
9	Sole Dispositive Power 28,242.00
10	Shared Dispositive Power 72,335.00

11

Aggregate amount beneficially owned by each reporting person

100,577.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

3.7 %

14

Type of Reporting Person (See Instructions)

IN

Comment for Type of Reporting Person:

* Includes 5,000 shares issuable upon exercise of vested stock options, and excludes 5,000 shares issuable upon exercise of unvested stock options, which vest on September 16, 2026, subject to satisfaction of time-based vesting criteria.

SCHEDULE 13D

Item 1.	Security and Issuer
(a)	Title of Class of Securities: Common Stock, par value $0.01 per share
(b)	Name of Issuer: C3IS INC.
(c)	Address of Issuer's Principal Executive Offices: 331 Kifissias Avenue, Kifissia, Athens, GREECE , 14561.
Item 1 Comment: AMENDMENT NO. 4 TO STATEMENT ON SCHEDULE 13D This Amendment No. 4 (this "Amendment No. 4") to Schedule 13D (originally filed on May 20, 2024, as amended by Amendment No. 1 on June 24, 2024, Amendment No. 2 on September 18, 2024, and Amendment No. 3 on October 1, 2025) relates to the common stock, par value $0.01 per share ("Common Stock"), of C3is Inc., a Marshall Islands corporation (the "Issuer"), and is being filed pursuant to a Joint Filing Agreement (attached as Exhibit 1 and incorporated herein by reference) by and between Flawless Management Inc., a Republic of the Marshall Islands corporation ("Flawless"), Arethusa Properties LTD, a British Virgin Islands company ("Arethusa"), and Harry N. Vafias in his personal capacity (sometimes collectively referred to as the "Reporting Persons"). Information given in response to each item below shall be deemed incorporated by reference in all other items below. Unless indicated otherwise, all items left blank remain unchanged, and any items which are amended below are deemed to amend and update the existing items in the Schedule 13D. All share amounts reflect the (1) 1-for-100 reverse split of the Common Stock effected by the Company at 11:59 pm, Eastern Time, on April 11, 2024, (2) 1-for-2.5 reverse split of the Common Stock effected by the Company at 11:59 pm, Eastern Time, on December 31, 2024; and (3) 1-for-6 reverse split of the Common Stock effected by the Company at 11:59 pm, Eastern Time, on April 3, 2025.
Item 3.	Source and Amount of Funds or Other Consideration
	Item 3 of the Statement is hereby amended by adding the following paragraphs to the end of Item 3: This Amendment No. 4 is being filed by the Reporting Persons to update the percentage of shares of Common Stock of the Company beneficially owned by the Reporting Persons to reflect dilution in percentage ownership based on the revised total number of outstanding shares of Common Stock reflecting the issuance of shares in connection with the Issuer's prospectus supplement filed with the Securities and Exchange Commission on October 9, 2025 and upon exercise of outstanding warrants of the Issuer. As a result of these transactions, the Reporting Persons no longer beneficially own more than 5% of the outstanding shares of Common Stock.
Item 4.	Purpose of Transaction
	The Reporting Persons acquired the securities described in this Schedule 13D for investment purposes and intend to review their investment in the Issuer on a continuing basis. Any Reporting Person may from time to time acquire additional securities of the Issuer, or retain or sell all or a portion of the shares then held by the Reporting Persons, in the open market, block trades, underwritten public offerings or privately negotiated transactions. Any actions any Reporting Person might undertake with respect to its investment in the Issuer may be made at any time and from time to time and will be dependent upon such Reporting Person's review of numerous factors, including, but not limited to: ongoing evaluation of the Issuer's business, financial condition, operations, prospects and strategic alternatives; price levels of the Issuer's securities; general market, industry and economic conditions; the relative attractiveness of alternative business and investment opportunities; tax considerations; liquidity of the Issuer's securities; and other factors and future developments. Mr. Vafias serves as the Non-Executive Chairman of the Issuer and therefore regularly engages in discussions with management of the Issuer, the board of directors of the Issuer, other shareholders of the Issuer and other relevant parties, which discussions may include matters ranging from the operations and conduct of the Issuer's business to considering or exploring extraordinary corporate transactions including the events listed in Items 4(a) through 4(j) of Schedule 13D. In connection with these discussions, the Reporting Persons may, either directly or through one or more affiliates, determine to take any available course of action or to take no course of action and may at any time and from time to time take steps to further or implement such course of action, including any of the events listed in Items 4(a) through 4(j) of Schedule 13D. Any action or actions the Reporting Persons may undertake with respect to their investment in the Issuer or the operations and conduct of the Issuer's business will be dependent upon the Reporting Persons' review of numerous factors, including those listed above, and the Reporting Persons specifically reserve the right to change their intentions, or to formulate plans and proposals, with respect to any or all of the matters described in this paragraph, subject to applicable law and regulations.
Item 5.	Interest in Securities of the Issuer
(a)	Item 5 is hereby amended and restated as follows: See Items 11 and 13 on the cover pages to this Statement for the aggregate number and percentage of the class of Common Stock owned by each Reporting Person.
(b)	Number of shares as to which each Reporting Person has: i. Sole power to vote or to direct the vote: See Item 7 on cover pages to this Statement. ii. Shared power to vote or to direct the vote: See Item 8 on cover pages to this Statement. iii. Sole power to dispose or direct the disposition: See Item 9 on cover pages to this Statement. iv. Shared power to dispose or direct the disposition: See Item 10 on cover pages to this Statement.
(c)	Except as set forth in Item 3 to this Schedule, no transactions in the Company's Common Stock by the Reporting Persons were effected in the past 60 days.
(d)	No other person is known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, the Common Stock beneficially owned by the Reporting Persons.
(e)	The Reporting Persons ceased to be the beneficial owner of more than five percent of the Issuer's common stock on October 9, 2025.
Item 7.	Material to be Filed as Exhibits.
	Item 7 is hereby amended to add the following exhibit: Exhibit 1: Joint Filing Agreement, dated October 10, 2025, among Flawless Management Inc., Arethusa Properties LTD and Harry N. Vafias.

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.

Flawless Management Inc.

Signature:	/s/ Harry N. Vafias
Name/Title:	Harry N. Vafias, President
Date:	10/10/2025

Arethusa Properties LTD

Signature:	/s/ Harry N. Vafias
Name/Title:	Harry N. Vafias, President
Date:	10/10/2025

Harry N. Vafias

Signature:	/s/ Harry N. Vafias
Name/Title:	Harry N. Vafias
Date:	10/10/2025

FAQ

How many C3is Inc. (CISS) shares do the reporting persons own?

The reporting persons collectively beneficially own 100,577 shares, representing 3.7% of the common stock.

Which reporting person holds the largest stake in CISS?

Arethusa Properties LTD beneficially owns 72,331 shares, equal to 2.7% of the class.

Did the reporting persons cease to be >5% owners of CISS?

Yes. The filing states the reporting persons no longer beneficially own more than 5% due to recent issuances and warrant exercises.

What is the stated purpose of the reporting persons' holdings in CISS?

The securities were acquired for investment purposes; the reporting persons may buy or sell from time to time and will review their investment on a continuing basis.

Does Harry N. Vafias have a role at C3is Inc. (CISS)?

Yes. Harry N. Vafias serves as the Non-Executive Chairman and is a reporting person in his personal capacity.