User blog comment:Jopjopjop/Volume 20 Spoilers/@comment-104.7.80.176-20151127185442/@comment-177.206.32.113-20151129015559

I assume it's because Asia was one of the first girls that met Issei and because she doesn't have any relationship with anyone else except for Issei and his parents. Remember, she became an orphan, her parents left her in the church and she suffered bad things in the beginning of the anime and above all, she didn't have any friends. Well, that's my opinion.