It's because Denji didn't consent to his private parts to be touched nor did he consent to be kissed. And since Yoru was suddenly doing this in Asa's body without her will, it was also SA on her part. Yoru used Asa's body to fulfill her neglected desires (kissing and groping) and when she switched back Asa had Denji's bodily fluids on her hand which was not by any means consensual for Asa. Based on Asa's previous reactions to sexual topics she is absolutely appalled by anything sexual so you might now remember how she reacts to anything related. So neither person communicated their willingness or indicated that it was consensual. Denji's hypersexuality doesn't indicate consent as well in case you might be confused as to why Denji didn't fight back. Denji's hypersexuality leads him to be easily taken advantage of and I know as someone who is the same as him it's difficult to reduce our sexuality and we could also experience no satisfaction from doing so as well. Just know that neither Denji or Asa would ever initiate something Yoru did.
This is genuine. Please don’t take this as me defending anything. But I don’t see the sexual assault, if someone could please kindly explain!! The reason I’m not quick to call sexual assault is because I don’t know how asa and Denji are going to react to this!! If they are both uncomfortable and disgusted then I will understand, but as for now….i don’t see sexual assault really?? So if someone can please explain that would be nice!!