The secondary male protagonist and the protagonist of the side-story manga, Future Diary: Paradox. One of Yuki's new friends at his new school, Aru is genius with an amazing investigation skills and wants to be a great detective. He becomes involve in the Diary Game to learn the mysteries surrounding it and protect Yuki. Aru is bisexual, as not only he is interested in Yuki, but shows interest for Minene and Tsubaki as well. As the games continue, Aru becomes suspicious of Yuno and tries to find out what secrets is she hiding from Yuki. He soon discovers Yuno's origins but also his own when he learns he was created by Deus as an "observer" to keep on eye on the contestant. Despite learning his origins, he continues to help Yuki and gives him the clue on Yuno's identity before she killed him.