User blog comment:UnlimitedMoeWorks/Touhou Characters and Their Likely Opponents/@comment-37388005-20190320041318

I got suggestions.

Flandre Scarlet:Sans (Undertale, they are both insanely hard bosses of Bullet Hell type games.), Jevil (Deltarune, Incredibly hard secret superbosses who were locked in the basements of their homes for their insanity), Marx (Kirby, they are insane and have rainbow light wings), Chara (Undertale, all they want is to KILL)

Reimu Hakurai:Frisk (Undertale, they both live in a world of monsters/youkai and are the protagonists of their respective game)

Cirno:Waluigi (Mario, they think they are the best, but they are not)