By a random god

After Dick Roman was killed by Dean,

All the Leviathans ended up in a place where time and place didn't exist.

They met a god, but not their "god"

What went down can be summed up as this: "I'm really bored and there is this boy, who I want to drop in with you lot, to protect him and make him you're leader so to speak"

The Leviathans, laughed at this, but the god gave a silver lining: "You will never feel hunger again, if you accept however you can only possess and mimick females from now on."

This wasn't a downside, while they thought about having a weak little human being their leader, the lower ranking members concluded that this human might have aboundance of empathy so he will probably be a lot more reasonable than Dick Roman was. (Who actually wasn't here)

The god let them have a peak at their charges soul. He was a kind soul, a bit perverted weak, but has a real softness in him. This actually opened the way for them to feel empathy, towards at least to the boy.

They will be always connected to his emotions. This will enable to them to maybe one day grow a "soul" so to speak.

Furthermore, if the lad dies, they die with him if they accept.

After a long debate between the members, they will spear this new world.

They will carve a life for their new boss. Anyone who tries to harm him will find why they are the Old Ones. They will devote their existence to him.

Oh, the boy in question has no idea that this will happen.

Oh, and it seems the god trolled them bit, because they are kinda scattered the moment they hit this new world.

AN.: The boy in question can be anyone, but instead of Issei I will use an OC