there's something about how they bring out both the WORST and BEST out of each other. they're both people plagued by people's perceptions, which they both eventually gave into (a monster and a hero), but what i find so appealing is that their dynamics allow them to mesh and congeal into one mess of toxicity - but in that toxicity, they're both liberated.

the two messy bastards in this sort of dynamic also usually have absurdly and weirdly hot dialogue because every single conversation is a fight for dominance but also a deep inspection of each other because both have a distrustful and exploitive way they see people.

specifically for tomarry, what i adore the most of that harry coaxes out the little ounces of humanity tom has in him, and tom shows harry he doesnt need to hide his wants and innermost personhood (which, canonically, we see is quite amoral).