How many movies have Rikiya Koyama and Sumiko Aihara collaborated on?

They have worked on 2 movies together! Their first movie together was Case Closed: The Crimson Love Letter (2017) while their highest rated movie together was Demon Slayer -Kimetsu no Yaiba- The Movie: Mugen Train (2020). They have not worked together since Demon Slayer -Kimetsu no Yaiba- The Movie: Mugen Train (2020).