Shuuji corrupted, warped, and trained her like a fucking monster. I'm glad Sumi's body repelled that monster's sperm as a contaminant. Man, I really hate him.
She's definitely a victim in some regards even if her choices weren't the best. The only person in life that gave a shit about her was an asshole who only wanted her for her body. If she was in a relationship with a much more caring person she definitely wouldn't end up as the person she is now and would probably make a loving caring partner. Said to see this type of development.
On a side note: Shuuji commenting that she reminds him of Sakuraba is an odd thing to say when you're fucking their brains out but you do you i guess