They hardly behave like normal humans do. I used the term broken as a relative adjective to describe that. It isn't necessarily a negative thing, but their mindsets certainly don't belong to the majority or accepted normalcy.

Yatori was brainwashed to be an Igsem heir from childhood, so much so that she would willingly kill Ikta (or so she says) at the cost of tossing away her self.

Ikta is so obsessed with being lazy because his father died doing his best to become a hero. His flightiness and apparent lack of desire to take on responsibilities and ties also stem from that.

They aren't exactly psychologically normal. If not for these issues, I'm pretty sure they'd be shacking up already. I mean come on, look at all their scenes together. They are closer than most spouses and certainly see each other as desirable. They even enjoy physical contact. They just have a barrier they can't cross because of the reasons I stated.

They are so valuable to each other that neither is willing to risk drastically changing the nature of their relationship and destroy that.