Nial intended to join the battle once again. However, he quickly noticed that there was not much left for him to do.
In fact, if he were to join the fight between Bella and Sabrina right now, his own sister may unintentionally consider him as a reinforcement of the Angel's Saintess. That was obviously nonsense because he was mantled in darkness and the Saintess released a holy aura that repelled his darkness, but it was always better to be safe than sorry.
Sabrina seemed to be faring greatly against Bella Morningstar, either way, much to Nial's surprise. Not that he was not happy about it. Even though Bella was in her Divine form, a state that elevated her strength manyfold, she didn't seem to be able to overwhelm Sabrina who wielded a mere mace.