User blog comment:B214/Volume 23 discussion blog/@comment-79.44.187.109-20170408222317/@comment-79.44.187.109-20170409001729

But Tiamat is not his wife or lover. lol

Sirzechs, Zeoticus and Issei cannot react with them (especially Zeoticus, since Venelana manages his harem so if she wants to he won't have sex ever again), that's the main reason.

Tiamat's threat is not taken lightly by Issei and Ddraig, so she must be very dangerous.

PS: I hope that she will become Ise's Queen. And maybe she could be the key to find one of the remaining two missing Longinus possessors. Ishibumi could kill two birds with one stone making both of them (Tiamat and the longinus possessor, if is a female) in Issei's team.