Aru Akise

A mysterious, fair-skinned, beautiful boy with a dream of becoming a world-class detective. He is always logical and calm. He is quick-witted, as shown when he neutralized the effects of the "Indiscriminate Diary" stolen by Hinata and Mao through strategy. He also has high physical abilities, demonstrated by his use of Aikido-like techniques to evade Yuno's attacks and carrying two people at once. He is a classmate of Yukiteru at Ume Sato Municipal Middle School and is investigating Yukiteru's surroundings. He finds Yukiteru cute, confesses his love for him, and is the only one in the story to genuinely unsettle Yuno.

He is suspected of being a Future Diary holder by the 10th due to tailing him and is targeted by the 10th's daughter, Hinata. After the battle with the 10th, he senses something suspicious about Yuno and investigates her. He actively intervenes in the Survival Game for Yukiteru, planning strategies for battles against the 8th's subordinates and searching for Yukiteru when he disappears with Yuno. He also exchanges information and discusses strategies with Detective Nishijima and Minene Uryu.

After the battle with the 11th, his true identity as an observer created by Deus to monitor the ever-changing future is revealed, and Deus attempts to erase him. However, he revives due to a preemptive move. With the cooperation of the 8th, he obtains the "Detective Diary," a Future Diary that predicts the actions of other diary holders, and stands in Yukiteru's way. However, he overestimates the power of the diary and falls into Yuno's trap, resulting in his death by decapitation. In his final moments, he conveys a certain truth to Yukiteru through his cellphone.

In "Paradox," he serves as the protagonist, taking Yukiteru's place. According to "Re:Dial," in the third world, he exists as an observer checking for abnormalities in the former Future Diary holders.