tbh, I doubt Osako even remotely understands, all she's seen is what's written. But that doesn't cover the grooming side of it, nor does it give her any information about his emotional state, and from what was hinted at, his mother didn't particularly care for him, so his sister was probably one of his only sources of familial love growing up. Mix that in with grooming and it's gonna be a clusterfuck of a traumatic past. Because socially, it just isn't treated the same when a male is groomed by a woman. If a man grooms a young girl or boy, it's seen as sickening. But when a woman does it, well the meme "noice" often rears its ugly head.
That causes a lot of dissociation between whether it was good or bad for the victim. And this is coming from someone with personal experience of something similar. Because even now, and it's like 27 years later, whilst I know it was wrong as fuck... well I don't feel like a 'victim' so fuck knows what it would be like for someone who's in Akira's position. When it was his sister, who's now dead.