I must be doing this wrong. I cant even find that on my device
Spoilers!!!
Rose is Momoko's daughter after she was experimented by her husband and his boss. If you find and have sex with her in the past timeline changes and Rose is no longer born. You can get her back by doing a little quest going through a portal visible in Momoko's quest. If all is done right you will be able to change timelines in your next playthrough from Aya, the girl that sits next to her.