Aru Akise (秋瀬 或, Akise Aru) is one of Yukiteru Amano's friends, and later becomes one of the main characters of the series. Akise is very intelligent and dreams to be a world famous detective when he gets older. Investigating the connections between Yuki and the diary owners, Akise becomes a close ally to Yuki, but an enemy and rival to Yuno Gasai. Akise quickly grows to love Yuki, and wishes for him to become God. He is the main character of the spin-off manga Future Diary: Paradox, where he and Muru Muru replace Yuki and Yuno in the survival game after Muru Muru accidentally kills Yuno Gasai while Yukiteru is injured.
Diary & Abilitieswhich allows him to read the predictions of other Diary Holders as well as their actions. This basically renders any opposing Diary useless, as he will always know the outcome. Despite this incredible advantage which easily makes this the most powerful Future Diary in the series, it does have weaknesses. For example, if one already knows what the predictions on his Diary .
For most of the series Akise relies on his great intellect to solve things. As the detective he aspires to be, Akise is quite smart and can deduce things easily with smart bits of information. For example, during the few times that Karyuudo sent his dogs on a killing spree, Akise was capable of tracking him. He also could figure out that Yuki's Random Diary worked based on his perspective, with seemingly no information at all.
Being a detective, he has strong ties with the police mostly with Masumi Nishijima; this gives him access to resources used by the police presumably information and also the policemen themselves, evidenced how he could figure out Yuki was a common under the multiple incidents with the Diary Holders, as well as have the police guard different places.
Akise has proven himself to be an expert in hand-to-hand and melee combat, being able to overpower Yuno even though she had pinned him down with a knife to his throat. While he is mostly seen without a weapon, when it comes to fighting he does have a preference for bludgeoning weapons like tonfa or a pipe. He has shown to be able to fight on par against Yuno on several occasions.
Future Diary: Paradox
The Tenth's Trap
The Seventh's Battle of Love
The Eleventh's Kingdom
The End Begins
With Kamado's help, Akise speaks directly with the dying Deus, asking him if it is possible to truly resurrect people. Deus answers the it is possible to resurrect the body, but the soul can never be brought back, therefore it is impossible to bring the dead back. With this new found knowledge, Akise realizes that Yuno had been lying to Yuki and decides to warn him; however Deus stops him and reveals another truth, that Akise is in fact a creation of Deus to serve as an observer in the game, whose duty was to obtain information. Akise denies that he was just a puppet and claims he has a will of his own, to which Deus challenges him to prove it. Akise says that he investigated both Karyuudo and Yuno out of his own will, but Deus says that Karyuudo was trying to evade the game and that Yuno is the most important person in the game. Deus gives one final chance to Akise, where Akise replies that his love for Yuki is his own, but Deus claims it is fake before banishing him. However Akise manages to turn back after successfully receiving his Detective Diary from Kamado, which Akise uses as evidence of his own free will to Deus. Amused, Deus agrees to let him do whatever he wishes.
Akise, is later found by Yuki and Yuno, and Akise says that the Eighth is in a safe place. Yuno asks where is she, and Akise mockingly says that he wants to talk with Yuki and that she should leave. Angered she stabs Akise, but proves futile as he has a protective vest. Yuno tries a stun-gun but Akise uses a rubber glove. Yuki and Yuno are shocked on how it is possible since Yuki's Diary confirms his death, and Akise reveals his Diary to them that renders theirs useless. Yuno urges Yuki to go after Kamado while she fights Akise, and he does so. Akise fights Yuno and wins with the help of his Detective Diary. However, Yuno manages to outsmart his diary by stabbing herself, to which Yuno threatens Akise that if left for dead, Yuki would hate him. Confused and shocked, Akise treats her wounds and heads as soon as possible to Yuki afterwards.
Akise uses this time to try to call out to Yuki, but he cannot make contact. He finds too late and much to his horror that Yuno had by this time tricked Yuki into killing his friends and rushes to Yuki desperately. There he finds that Yuki has killed all the others in an attempt to kill Kamado.
During his last attempt to convince Yuki about abandoning Yuno as he believes Yuno will kill him to become god. Yuno arrives wounded and tells Akise to get away from Yuki, but Akise kisses Yuki provoking Yuno. He fights once more against her ready to destroy her Diary which he does, however and much to his shock, Yuno is still alive and slices his throat. Upon reading the entry on the destroyed Diary, he realizes that what he destroyed was the real Yuno's Diary instead of hers, but given that the real Yuno was never a participant, it is impossible that she would have a Diary. Pondering the rules of the game and the power of the Diaries, he finally discovers Yuno's secret.
Akise, who had discovered Yuno's secret, tries to tell Yuki, but finds himself unable to speak due to his throat injury. He is then decapitated by Yuno while trying to show Yuki his diary's screen, on which he had written his discovery about Yuno. Even as his head flies into the air, spurting blood, his body somehow manages to walk to Yuki, show him the screen of his diary, and reveal Yuno Gasai's secret.
Third World: OVA Redial
After the incident in the Second World, Aru Akise works for Deus as an observer for the twelve diary holder. Third World is living in peace without the incident and massacre that happened in Second World. Deus' power is still dying yet, he hasn't found a new God to take his place and even planned out a new game.
Akise, Yuno, Mao, Hinata, Kosaka and Reisuke (being his assistant) were all out for Summer class excursion when Yuno realises that something is missing from her. Akise reports this to Deus.
Yuno was sitting on her bed when a voice started talking to her. She then started talking to her and brought her to the God's realm of Time and Space. Meanwhile, the Third World Murmur was talking to Deus when she suddenly sensed someone got in the forbidden area. Yuno started walking to the platform, following the voice in her head until third world Murmur stopped her. Uryuu used her powers (obtained from the Second World Deus) to stop third world Murmur from interfering with Yuno.
After Yuno got past third world Murmur, she sees Akise standing in the middle blocking her way. Akise starts telling her about her First World's personality and what she did to the Second World. Akise charges with a katana at Yuno, Yuno stops him and falls together on top of him. Yuno took the katana and kept walking until she saw the sphere, where First World Yuno locked Yukiteru (a world created by her for Yukiteru's wishes and desires to happen). From there, she saw the first world Murmur. Murmur starts crying and talks about her old master, First World Yuno, to her and how her memories shouldn't vanish in vain. Yuno accepts her First World memories.
Meanwhile, Yukiteru's Future Random Diary bleeps and show 'Yuno went to see Yukiteru'. Yuno went to the Second World's realm and hugs Yukiteru. Third World Deus made Yuno to be the third world's Goddess, making a pathway for Yukiteru and Yuno's realms.
- Aru's character theme song is "Song of A Certain Truth" by Alice Rokugen.
- His given name, Aru, means "exist", which is likely to be a subtle hint to Aru's true origins.
- In Paradox, Aru's brief alteration of history allows him to create a large alliance made out of most of the diary owners - Keigo Kurusu, Reisuke Houjou, Tsubaki Kasugano, Marco Ikusaba and Ai Mikami, Kamado Ueshita being represented by Orin Miyashiro, and Yomotsu Hirasaka. He never meets Karyuudo Tsukishima and John Bacchus, kills Takao Hiyama and fights Minene Uryu.
- In the Japanese dub of the anime, Aru's voice is deeper that Yuki's. However, this is reversed in the English dub.
- Akise loves Yukiteru. He kissed Yukiteru to make Yuno jealous and charge at him. When Akise tells Deus about his will, Deus tells him it was all created and planned out by him. When Akise tells Deus that he loves Yukiteru, Deus tells him it was also part of his plan.
- Third World Akise is called an observer by Third World Murmur and Deus.
- He was a diary apprentice in the Second World, and he used Eight's server to use this. His diary is called the Detective Diary, which can resolve an incident, or tell the truth.
- In the Third World, Tsubaki has her eyes on him and is a complete stalker.
- Akise Aru is very similar to Kaworu Nagisa from the Evangelion franchise, particularly their love for the protagonist & close relationships with them. Coincidentally, they are both voiced by Akira Ishida.