Sekiro uses one profile-level S0000.sl2 file, so a file replacement can roll back several in-game slots at once. The safest routine is therefore simple but strict: close the game, copy the whole account-ID directory, keep more than one dated generation, and only then experiment. Steam Cloud is another revision source; if a manual restore appears to revert itself, solve the synchronization conflict before overwriting the folder again.
Known Sekiro: Shadows Die Twice save-file structure
The researched filename or folder pattern is S0000.sl2. File-extension context: .sl2 The documented format notes are: The Steam PC profile is a single S0000.sl2 container under an account-ID directory. Multiple in-game slots are not separate operating-system files.
Why an extension is not enough
A save filename can identify a likely container, but it does not prove the internal schema, game version, checksum rules, encryption state, or editability. One .sl2 container can hold multiple in-game slots. File-level replacement rolls back the profile container, not one isolated character slot. SaveEditor therefore separates file identification from Tool compatibility and only labels a game-specific Tool Verified when its exact profile/version evidence passes the runtime gate.
Where the format is stored
PC save locations: Windows: %APPDATA%Sekiro<user-id>S0000.sl2 | Linux / Steam Play: Steam Play: <SteamLibrary-folder>/steamapps/compatdata/814380/pfx/. Storefront context: Steam. The user-ID directory is part of the save context. Do not assume a copied S0000.sl2 belongs to the active Steam identity. This matters because two releases can use different containers or companion files even when the visible slot name is similar.
Back up before inspecting or editing
Copy the entire Sekiro account-ID folder with the game closed. Keep multiple dated versions because the game continually updates the same container. A read-only viewer is lower risk than a writer, but the live save should still be copied first. Cloud context also matters: Steam Cloud is documented. Keep the original bytes available so any experiment can be reversed without relying on a cloud service or automatic backup.
What this reference does not claim
This page does not infer an undocumented checksum algorithm, encryption key, compression layer, or cross-store conversion from the file extension. Troubleshooting evidence: If a restore is replaced on launch, compare Steam Cloud state and modification times. Keep the original local file before testing any imported container. Those questions require a verified parser/profile or a game-specific source, not a generic format guess.
Verification context: Windows path, S0000.sl2 filename, Steam Play behavior, and Steam Cloud support were reviewed against current PCGamingWiki coverage.