I don't know about specific fics, but independent!Harry or time-travel!Harry basically are this.

Alternatively, you could look for:

Any standard Snape/Lily fic (guy calls girl racial slur, is involved in a terrorist group that aims for the genocide of every person like her. Girl: but he is misunderstood, or something like that)

Any old Dramione fic (see above)

Any old Hermione/Death Eater fic (see both above)

Any Drarry fic (See above, replace girl with son of girl)

Any HP/SE fic (See above)

Any HP/LV or HP/TR or HP/any generic DE fic (boy falls in loooooove with parents' murderer who incidentally wants to murder him as well)

For all the above types, toxicity is the starting point. You can always delve further through this for the character understanding that he/she is in a toxic relationship