'Both of them...are in a vulnerable state...a state where I can kill them both, right here right now.'
Oumu thought as he looked down at Lucifer, who was buckling down, and Nocturnal Phantom, who couldn't even be seen anymore.
Of course, Oumu was tempted by this situation. The Warmester Denoble House is the house that Oumu pledged his loyalty to.
The Patriarch of the Warmester Denoble House is the man to who Oumu pledged his loyalty.
It was only natural that...if given the chance, Oumu would want to avenge his master and bring justice to the Warmester Denoble House.
And even though he is a friend to Rouge, he would also want to make Rouge meet justice and bring him down from his current position that wasn't even meant to be his.
Of course, just because Oumu really did agree to betray the Warmester Denoble House, it's not like...he could just ignore the temptation that he was seeing right now.