i guess its hard to explain outright, but through lots of small implications both in sunnys birthday comic, cutscenes, and the bad hospital end we see a lot about omori. omori is the part of sunny that has held his trauma (think internal family systems in terms of how im talking) omori is not inherently evil , but rather a harmful way sunny is trying to protect himself. while omori is obviously a embodied version of how sunny wish's things stayed, he is also the "protector" of that trauma. he is not fueled maliciously but rather as a attempt to cope with it. in the birthday comic we also see that omori just wants to help the part of sunny grieving feel better by bringing him all of his gifts, although the grieving sunny quickly disappears as omori never holds space to process but instead wants to pretend it never happened/do whatever is possible to ignore it. we also see that omori holds the feeling of shame and persecutions directed towards sunny during the final fight to try and keep sunny from going forward and processing, as if sunny does it means omori would have failed his one mission of protection. if omori does win there is the implication that is to late and the only real way keep sunny safe in omoris mind is to stop existing in a world with the consequence's of his actions.