pretty sure ran would also make the cut, shes literally a super robot. its like stockfish but now its shikigamifish.
yukaris also pretty smart and does scheme a lot, and patchy is not only smart but could probably also memorize every grandmaster game ever played.
and one last question is whether were factoring in abilities. im assuming not since that isnt exactly whos the best at chess but rather who can manipulate chess in their favour, but if we are running abilities into the mix, a few characters i can think of are sakuya, seija, and keine.
I ran a Touhou Sort with my audience and sorted every character from worst to best. For top five best we had:
1. Miko
2. Eirin
3. Momiji
4. Alice
4 (Was a Tie). Mamizou
For five worst we had:
5. Rumia
4. Futo (Always falls for the 4 move checkmate)
3. Koishi
2. Fortuneteller (is dead)
1. Shion
What Touhou characters do you all think are the best and worst at Chess?