SCHEDULE 13D/A

C3IS INC

Common Stock, par value $0.01 per share · CUSIP: Y18284169

Event date: 2025-09-29

Reporting persons may disclose overlapping interests. Their amounts are shown individually and are not added into a filing total.

Filing-level shares

Unavailable

Percent of class

Unavailable

• Flawless Management Inc.Reported CIK 0001328920

  Shares: 4 · Class: 0.01%

• Arethusa Properties LTDReported CIK 0002004014

  Shares: 72,331 · Class: 4.5%

• Harry N. Vafias

  Shares: 100,577 · Class: 6.3%

Amounts are as disclosed in this filing. Schedule type alone does not establish investment intent.