Surprising, even by Google's standards. DDLC is a violent game but not much more. What app store rule exactly is it breaking?
"Violent"? Do you consider news reporting to be violent too? This isn't remotely in the league of all the shooter games you can find on the store.
There are countless games on the store that let you kill endless hordes of humans in detail...
Self-harm (especially when depicting minors) has special standards. The recent court losses on child safety for Meta and YouTube probably led to this.