All the X-Men: First Class Cherik comics I found at Comiket. There was a 5th book that looked like it had a lot of chibi Charles and Erik, but sadly it was all sold out!
Gimme Gimme What I Need: Charles wakes up in the middle of the night because he can sense Erik is not well. He finds him on the floor, crying manly tears of manliness. He then proceeds to cheer him up in an NC-17 rated way.
Stay Darling: Erik loses their game of chess, so he has to undress for Charles, which makes him feel rather self conscious, and Charles very smug.
Giant-size Ashige: Several short stories by different artists, all about Charles and/or Erik, with one very sweet one where Erik wants to hold Charles’ hand in public cos that’s what all the other couples are doing.
Blind: Sad little book that starts with Cherik meeting, getting closer, getting very close, and then the divorce.