"Negative emotions bad" is... I mean, what level of negative emotions? I'm not into stories where the whole point is negative emotions, but even when that's not the case, they do still tend to contain some.

But I think it's safe to recommend Not the intended use, a Castlevania fanfic (with mild SMT crossovers) in which Soma Cruz finds ways to use his various demon souls for mundane purposes. Like using the Ghoul soul to save money on groceries.