for me he is a Wife but he is not a True Fufu Wife(TM) on account of him being a Neurotic Catholic.

True Fufu Wife(TM) has a sense of peculiarity to them. they twist their own morality; their logic is often known only them, following pathways that are a world onto itself. both people and rules bend to fit them. they flit among the masses as some sort of almost-whimsical outlier.

sunday has some fufu traits, but his catholicism inhibits the rest. catholicism restrains, and sunday restrains himself first and foremost. there is a sense of jaggedness to his neuroticism and obsessiveness that almost seems clumsy, because his control issues are startlingly obvious. his self-deprivation is also obvious for all to see, and that renders him and his motives less murky than True Fufu Wife(TM)'s might have been.

i keep saying that he is essentially an ayato expy, but their backstories are deliciously contrasting—ayato is as close to an agnostic as one can be in a land literally ruled by a god, whereas sunday twists himself into painful shapes in deference of a long-dead god. their core traits are extremely similar in ways that matter to my dick, but ayato actually has the space to harness his True Fufuness and sunday just... doesn't.