User blog comment:B214/Volume 23 discussion blog/@comment-2208155-20170317184654/@comment-9595671-20170317203024

Actually the swimsuit could do it, it just needs to play the "leave a little to the imagination" card.

That and you have to remember that he saw them while in Heaven, and in Heaven such thoughts are instantly nullified by a system put in place.

That same restriction doesn't apply outside of Heaven, so Issei can let it out his excitement without any worries either.