https://www.gamespot.com/articles/sekiro-shadows-die-twice-originally-started-as-a-t/1100-6461426/

From Software rose to prominence with Dark Souls and Bloodborne, but the studio's newest title, Sekiro: Shadows Die Twice, is a marked departure from its previous works. The game still retains the unforgiving difficulty and deep combat system that have become From Software's hallmarks, but it trades the established worlds of Dark Souls and Bloodborne for an entirely original one based on feudal Japan. However, it seems Sekiro wasn't always intended to be a new IP.

Speaking to Games Industry, From Software community manager Yasuhiro Kitao revealed that Sekiro was originally planned as a new installment of Tenchu, the studio's long-dormant stealth-action ninja series. "When we originally set out to create something different from Dark Souls and our previous titles, we thought it would be interesting to make a Japanese themed game. So from that we started going in the direction of the shinobi and ninja, and of course Tenchu was an IP with that history; that was the original impetus for this project," Kitao explained.