Well, who are you saying was assaulted in that scenario? The unconscious Kirishima sleepwalking his way through that, or Yoshino who didn't truly force herself away until after she truly panicked due to the unfamiliar sensations she was experiencing?
It's not about romanticizing assault either.
One method authors sometimes use when one of the characters is basically a blank page when it comes to sex is put them in a situation where they experience sensations that give them a hint as to what that might be like. Here, the goal was to give Yoshino a hint of what being intimate feels like. So it's not happening now, but it will happen in the future (many are hoping it won't be before their college years). The part where she shuddered as he touched her was a call back to the reaction she had to him in the lotion scene on chapter 25.2. A shiver down the spine type of thing.
Perfect explanation
Not at the romanticized sexual assault at chap 38