The fight was a little rushed, romantica would be more useful, she was supposed to be the one casting water wall on the frozen spell on the previous chapter and it would be really key on discovering the homunculus weakness, and it's not just mana, it's more like he dont do well with consecutive deaths and mana used, it wave to be killed at least 2 times and on the last desir attack it dont got tired but mutilated, I think it had something to do with the PG status of the comic, the novel is way more brutal