namco x capcom is the second in a series of four games, with namco super wars before, and the two project x zone games after it.
street fighter 2010 on the nes is about ken as a cyborg in the future.
wolf and jeffrey from virtua fighter appear in a few sega-developed all japan pro wrestling games
there’s a samurai shodown rpg on neo geo cd. kyo kusanagi and athena asamiya both have adventure games on ps1 (athena’s is also a tie in to a live action tv series!), and i think nakoruru has two on dreamcast. plus there are a bunch of dating games starring various snk characters, aimed at men and women.
there are a couple of eternal champions spin-offs, but the only one i can remember the name of off the top of my head is chicago syndicate
princess clara daisakusen is a shooting game starting a character from the power instinct games
and there’s also super puzzle fighter and psychic force puzzle taisen
Maybe this doesn’t count because they weren’t originally fighting game characters, but there were a few SNES belt scroller type games that basically used marvel vs Capcom sprites
This is a bit of a stretch but in the Final Fight port for the GBA (Final Fight One) you unlock a mode where you play as Cody and Guy but in their Street Fighter Alpha sprites. It looks real weird and out of place!
Somewhat fun though is that this version added a bunch of dialogue scenes during the course of the game when meeting bosses and such and when playing as their fighting game sprites Cody and Guy will act as if they’ve time travelled back in time to relive the events of the game.
gonna make the biggest stretch with this, but JCVD is in Street Fighter The Movie (The Game), credited as such, then shows up in 2021 in some game called Warpath:
I guess there was a samurai shodown turn-based RPG? Shinsetsu Samurai Spirits Bushido Retsuden. Sorry to say I got this from a top 10 list on “thegamer.com”
Similarly off of this, the GBA Konami Krazy Racers has Beartank from Rakugakids; looks like he didn’t make it to the mobile sequel. Beartank also shows up in Pop’n Music.