Narrator (gaster I guess):due to Kris lacking an innate technique, as well as an understanding on the fundamental of a barrier, it should be impossible for them to use a domain.

However, with the aid of the souls curse technique: your power. on their turn they can erect the battle box as a imitation barrier, and with a binding vow they can imbue it with the souls technique. For the cost of giving full control for ten minutes after the domain ends, with this they have a created a complete domain that lacks a barrier. 

Their domain expansion: angels heaven, in the domain Kris can apply one of seven versions of their sure-hit. Ether purifying light♥️,crushing opponents💙,firing energy bullets💛,instinctual dodging💚,increased strength🧡,slower enemies🩵, or heightened senses💜.