As
@kurousagi75 said, this is nowhere near as horrific as what happened in real life. Not only she was gangraped, but also tortured in the vilest and cruelest ways possible.
The girl was ultimately killed, and her body dumped in a drum and filled with concrete. The culprit also are free to this day after a light sentence. Furuta's grave was vandalized by the families of one of the culprits as "she ruined their son's life".
It really feels something out of someon's sick imagination... but here life outdoes reality.
And sadly, there is a manga which is far more explicit than this one in depicting the case. I recommend to stay away from it as much as possible.
I don't really know what to think of this manga. It's not really faithful and doesn't really get any sort of teaching/point across.