Self-sovereign identity (1) has the concept of a Decentralized identifier (2) at its core and, as far as I understand it, most use cases rely on the DIDs being stored on a distributed ledger, which is generally Blockchain.

Disclaimer: not a crypto or blockchain promoter but the above is my understanding of SSI.

(1) https://en.m.wikipedia.org/wiki/Self-sovereign_identity

(2) https://www.w3.org/TR/did-core/