Enryu came as an agent of outside gods. He was acting on behalf of his gods, rather than as a private person, when he entered the tower.

Therefore, we can infer that everything he's done in the tower was in strict accordance with the guideline given to him by the outside gods. We can assume that from the deal that Arlene made with the outside gods, Enryu was instructed to go into the tower specifically to perform the following sequence of action and NOTHING ELSE:

1/ deliver the speech he did to death floor resident.

2/ kill guardian

3/ leave thorn behind

It can be assumed that Enryu's power was granted to him by the outside gods, so it is only nature for him to follow their instructions properly.

Why didn't the outside god interfere even more? Arlene made a deal with the outside gods, offering her dead son, and the outside gods accepted. Enryu's appearance in the tower, therefore, could be infer to mean that the outside gods was delivering their end of the bargain they had with Arlene.