After the embarrassing moment of not knowing what the blood oath was, he consulted with his advisors first before they came to an agreement. He didn't want to drag them into something they didn't want, he did offer them refuge after all.
The terms of the agreement were pretty simple, anyone whom tried betrayal from either of the kingdoms would be receive divine punishment of instant death, this obviously included those who would try to kill.
Something that made Levi hesitate greatly since he still needed to feed. But he could do so without killing, a year at most, he was sure he could handle it.
If it got worse he could always branch out to the other kingdoms, he'd always wanted to scout them and see the different cultures. And the fact that he'd never had their blood excited him, a little.
Levi's only concern was the humans strength by the looks of things they weren't all that strong, the three kingdoms walking all over them proved that much about them.
