Rui is the main character of the mecha anime Infinite Divine Machine Mono Magia. He pilots a giant robot called the Gigas Machina and shows up at his creator's house in the real world alongside it.
In his own world, Rui was a child soldier who spent his entire life in combat—he never got to experience normal kid stuff like dating or just hanging out. So he's genuinely relieved to find himself somewhere peaceful for once. That said, he's got a notable attraction to girls younger than him, which is. a thing about his character.
Content compiled by AnimeList.moe from publicly available sources.