has she done something truly evil, tho? it's mean and kind of shitty, but it's not like she manipulated them to get something out of them, it's more like she really doesn't understand how she could ever interact with people in a different way. She got nothing out of that except a momentary feeling of "i won this interaction".
She did manipulate them to get something out of them: emotional regulation of her low self esteem. She manipulated them to think she was interested in them romantically so they would show her romantic affection in return. She feels unwanted because of the loveless environment of her upbringing, and she copes with it by manipulating as many guys as possible, guys that she doesn't value and doesn't respect, into liking her just to prove to herself that she's loveable. Then when they realized what's going on, she discards them.
She does so with absolutely no regard for the feelings of the guys she's manipulating; she doesn't consider the kind of pain she's causing them when they realize she never liked them let alone respected them and the trust issues she's creating in them around romantic love.
She's narcissistic. She's getting her emotional needs met no matter how many others she has to hurt. She's not "evil" in the cartoon villain sense that she hurts people just for fun, but she's "evil" in the very realistic sense that she doesn't care who she hurts and does what she does to cope with her own pain knowing it will hurt them. I can sympathize with her, but she's still responsible for the pain she's caused.
Edit: Just to clarify, I do not think Yasaka is truly "evil," hence the quotation marks. I'm responding to rabidfish's use of the word and pointing out that what she and other narcissists do doesn't have to be evil with a capital E or done for material gain for it to be doing harm that should be taken seriously. Also, when I say she's still responsible, I don't mean she needs to be held responsible but just that she is still the cause of that harm, whether her reasons are sympathetic or not and whether she is concious of the harm she's doing or not.