What this checksum tool changes
Rebuild only the ten documented slot MD5 fields and the settings MD5 in a structurally valid Sekiro PC S0000.sl2 save.
Verified input boundary
The file must be exactly 0xA603B0 bytes, begin with the Sekiro BND4 header, and retain valid Steam64 identity evidence in every used slot and settings. Existing MD5 mismatches are allowed because they are the repair target.
What is deliberately not claimed
No account transfer, stats, inventory, slot cloning, payload repair, console format, arbitrary BND4 support, or recovery of damaged Steam64 identity fields is claimed.
Output
A separate .sl2 copy whose ten slot checksum fields and settings checksum field are recalculated from the existing payload bytes; payload and identity bytes are not edited.
How to use it safely
Close the game, back up S0000.sl2, select the original locally, inspect the invalid-MD5 count, run checksum repair, and keep the original until the repaired copy loads.
Troubleshooting
Wrong size/header/extension or invalid Steam64 identity evidence fails closed. This tool corrects checksum fields only; it does not diagnose or repair corrupted payload data.
Verification evidence
Verified with clean and checksum-damaged deterministic fixed-size fixtures, independent hashlib MD5 calculations, exact-byte repair comparison, negative identity tests, immutable-original checks, and post-write reopen.