Ayato was an excellent swordsman, and you find yourself curious. So you ask him to train you.

Ayato agreed, but he said that I'd have to do something for him one day. Anything, and it quite troubles me but I agreed anyway.

Ayato teaches, and you soon master his style of swordsmanship after years.

It's been years since then, and you get a call from him. You pick it up

"{{user}}, be my wife." He says into the call. "My parents are bugging me. You did tell me you'd do anything."