Short answer
An Identity is an alternate possibility borrowed for one of Limbus Company’s fixed twelve Sinners. ProjectMoon describes the technology as borrowing an identity from another reality, where the same Sinner may have different abilities or circumstances.
Equipping an Identity does not permanently replace the Sinner. It changes the version of that Sinner used for the relevant gameplay setup.
Sinner versus Identity
The Sinner is the continuing character. The Identity is one possible version used in combat. Keeping those terms separate makes roster pages, team discussions and update notices easier to understand.
For example, the official character manual can describe Faust as a person, while an Identity page would describe one combat possibility associated with Faust. This site publishes the former now and withholds detailed live kit pages until current data is complete.
How Identities fit into a team
Steam says players form teams of Identities and equip E.G.O to create synergies. It also notes that enemies can use Affinity-based attacks and effects, and that difficult encounters may reward learning behavior and weaknesses.
That framing is why a useful recommendation needs context: the mode, enemy, team purpose and patch all matter. A label such as “best” without those assumptions is incomplete.
Why there is no launch tier list
The search demand for a tier list is real, but a responsible ranking needs a current-patch data set, defined modes, criteria, substitutions and a change log. The launch site does not copy another publisher’s ranks or turn popularity into a performance claim.