User blog comment:TrueHeavenlyDragonGod/Issei's belongings/@comment-23847729-20140201041924

I would say Rias. Sure, she is his master, but she is also his lover.

I mean, she was like throwing herself to Ise in Volume 10 when they were alone in the sauna.

And of course, her oppai belong to him as well. :I