Reisuke Houjou

Reisuke Houjou is the Fifth diary owner and the youngest of the twelve. While appearing as a harmless four-year old, Reisuke is a master strategist and forces Yukiteru Amano and Yuno Gasai to a deadly death game in Yuki's own house. He often is seen with a pair of hand puppets, and owns the "Hyper Vision Diary".

Personality
To the unsuspecting eye, Reisuke appears to be just an ordinary toddler - innocent, bright, curious and polite. However, Reisuke is really a complex individual despite being a four-year old. His parents were implied to be either abusive or neglectful, often fighting and more interested in their own personal hobbies (shopping and gambling). Because of this Reisuke seemingly grew to dislike his parents and learnt to take care of himself. However, his parents were at least on one occasion nice enough to buy him a pair of handpuppets, both stylised to resemble a man and a woman, seemingly becoming faux replacements for Reisuke's parents. Reisuke often talks through the puppets and use them for other means, and he portrays them as the ideal parents he would have preferred to have had.

Reisuke uses his young appearance and age to fool people, acting like the normal toddler he should be. However, beneath that he is really a sadistic, creepy and cruel person, and very intelligent for his age. Despite this, he still has the mindset of a child, referring to Yuki and Yuno as "big brother" and "big sister". He is particularly enthralled by the survival game, seeing it as just that, a game, and has great fun in "playing" against Yukiteru Amano and Yuno Gasai.

Reisuke's goal to win is to become a "super elite", presumably his view of a God or a better person than his parents were. Despite his goal and behaviour, Reisuke does show some signs of kindness. He spares Yuki's mother Rea Amano from being killed, having enjoyed his time with her and even considered his whole time with Yuki, Yuno and Rea to be the family life he had desired. While at first he considers killing Yuki and Yuno to avenge his parents, he quickly ditches the idea. However, as revealed in Future Diary: Mosaic, a spin-off story focusing on Minene Uryu, Reisuke is revealed to be upset by his parents' death and even abandons his handpuppets at one point after Minene points out to him how he should act like a child.

Diary & Abilities
His Diary is the Hyper Vision Diary, which takes form of a colouring book. The diary is limited, only able to make three predictions a day during the main times of the day (morning, afternoon, evening). However, this gives Reisuke plenty of time to plan out his strategies for the survival game and carry out three attacks once for each event which given his appearance, he is also successful to mask. Because his diary is unable to predict immediate events, that means he can at most carry 3 attacks per day without any sort of potential risk. Despite this his Diary entries reflected as pictures with a small summary do change when the future changes.

While his Diary itself may seem limited, Reisuke can more than make up for it with his great intellect for a 5 years old boy. He has proven himself an expert of chemistry and physics, being more than capable of manipulating a wide array of substances to create poisonous material, which he can either inject or booby trap in the form a gas trap, which he once used to trick Yukiteru to open. Along with his use of poisons he's cautious enough to carry and use a Gas Mask and also the antidote. Reisuke is also smart enough to use electricity with rubber gloves to avoid the danger, and was almost successful in electrocuting Yuno while bathing, having previously filled the bathub with salt to increase the conductivity.

During his time in the Amano House, he proved himself a skilled infiltrator who uses his looks to deceive others as well as study the house so carefully that he booby-trapped the whole house before filling it with poisonous gas, with tacks on the floor, or using decoys to fool Yuno into where he was hiding while she ventured the house, and almost killed her by mixing water and electricity into the stairs as she was barefoot.

Being the kid he is, it is really dificult to truly measure his chances of winning the game when compared to other participants. He's however comparatively speaking given his age, the smartest of the participants.

Path to Revenge
Reisuke's parents were murdered by Yuno during the incident at the Sacred Eye temple, likely two of the followers hypnotised by Yomotsu Hirasaka to kill Tsubaki Kasugano. Reisuke survived the incident and kept in a hospital for a time. Minene visited the hospital to get a fake eye after losing her right eye, noting Reisuke's presence. After getting the replacement and leaving, Minene spots Reisuke trying to gain some potassium cyanide from a storeroom. Minene rescues Reisuke from falling but is baffled when she finds a list of several dangerous items for a potential chance at revenge. Minene, holding Reisuke's puppets, teases him and tells him to seek revenge, suggesting he takes a nap with his puppets as if they were his parents. Reisuke suddenly starts crying and angrily runs off, claiming he never shared a bed with his parents.

Having left his puppets behind, Minene decides to give them back to Reisuke and also help him gather the items he wants, despite her opinions on revenge. She goes on a wild goose chase trying to give Reisuke back his puppets, but he continues to leave them behind. The other items including acid from a chrome plating factory, a gas mask, a stun gun, and money, although Reisuke ditches the money after Minene's attempt to rob a bank ends in disaster. Reisuke then visits Sakurami Elementary School, where the victims of the temple incident have been stored in the gym. Reisuke identifies the bodies of his parents, kept in bodybags. Criticizing them for being laid side by side, which they never did when alive, Reisuke then lays down in-between them and recalls the time where his parents bought him his handpuppets, causing Reisuke to cry himself to sleep. Minene arrives and successfully returns his puppets to him before leaving.

The Death Game
Reisuke managed to "infiltrate" Yuki's house, under the care of Yuki's mother Rea for several days until he was put up for adoption. Reisuke put on his innocent act, introducing himself to Yuki and Yuno and confirming who they are through his puppets. Reisuke immediately shows signs of hostilities, drawing a facemask of Yuno, and runs to give it to her only to trip over a rug and falls onto Yuno, nearly stabbing her with a pair of scissors. However, Yuno knew what was coming and blocks the attempt with a pillow.

Reisuke goes to the bathroom, locking himself in and plans his next move, involving a pair of syringes carrying toxic substances. At lunch, Reisuke prepares a salad and injects the toxins into tomatoes for Yuki and Yuno to digest. As Yuki is about to eat his, Yuno stops him, claiming the tomato's weight is off slightly, claiming to be concerned for Yuki's health and removes the salad. Yuno implies to Reisuke she is on to him, amazing Reisuke. Upping his game, Reisuke plans to electrocute Yuno by creating a strong current in a bath, and then plans to kill her using live wires from a washing machine. Reisuke tries to take a bath with Yuno, but Yuki realises what is about to happen and shuts off the power before Reisuke can electrocute Yuno.

Yuki informed Kurusu of Reisuke's presence, who then informed Minene to keep an eye on things. Whilst Yuki searched for Reisuke's diary, Yuno went for the more dangerous option to kill Reisuke with a knife. Reisuke acts normally, enjoying his time spent with Rea whilst keeping an eye on Yuki and Yuno as they continue to look for his diary.

Yuno eventually becomes impatient and attacks Reisuke with a hammer, accidentally knocking out Rea. The day before, Reisuke mailed his diary to himself in a parcel. Yuki snatched the parcel and opened it, only to release a toxic gas into the house. Yuki quickly succumbs to it, Yuno dragging him into the bathroom whilst Reisuke celebrates his victory. Reisuke urges Yuno to play a deathmatch of hide and seek. If she finds him, he will give her the antidote to the gas, and if she loses, she and Yuki will die. Yuki objects, but Reisuke reveals he placed Rea outside to spare her. Yuno searches the house, finding it boobytrapped. In the anime, Reisuke has somehow taped all the windows shut despite his size, forcing Yuno to break a window to breathe.

Yuno eventually goes upstairs, finding Reisuke waiting for her, sitting on an overturned chair. However, Reisuke has left the taps in the upstairs bathroom running and the water quickly covers the landing and gushes down the stairs. Reisuke pulls out the stun gun Minene got him and electrocutes the water, electrocuting Yuno and causing her to fall down the stairs. In the anime, Reisuke used a lamp's lightbulb to electrocute Yuno. Curious of Yuno's actions, Reisuke asks her why she protects Yuki, realising despite being electrocuted she managed to hold her breath. Yuno replies that she simply loves Yuki, Reisuke deciding to kill her. Yuki suddenly charges in, knocks Reisuke away and rescues Yuno by kissing her, whilst performing mouth-to-mouth. Yuki faints and falls down the stairs, Yuno grabbing her knife and confronting Reisuke.

The next scene shows Yuno has stabbed Reisuke in the chest with the knife. Reisuke hands over the antidote. However, he tells Yuno in the end, only one diary owner can win the game and sooner or later she will have to fight and kill Yuki. Yuno is shocked by this, Reisuke disappearing from existence, putting his support behind her to win. His diary's final entries reveals whilst Reisuke died, he was happy with the outcome. Yuno succumbs to the gas, but Minene appears, healing Yuki and Yuno with the antidote.

Kurusu cleared up the situation using a cover story, although what he told Rea was unknown.

Future Diary: Paradox
In the spin-off Future Diary: Paradox, Aru Akise and Muru Muru temporarily replace Yuki and Yuno after Muru Muru accidentally killed Yuno, causing Yuki to be wounded by Takao Hiyama. During the incident at the Sacred Eye temple, Akise decides to alter the future by saving Tsubaki Kasugano from her fated death, escaping the temple with her and coincidentally landing in the convertible Reisuke is sitting in. Akise drives the car to safety with Reisuke coming along for the ride, and he agrees to aid Akise and Tsubaki in their plan to expose the temple's second Funatsu as the murderer of Tsubaki's parents.

Because his parents are still alive, Reisuke is shown to be much more cheerful and kind, running off to find Yomotsu Hirasaka whilst Akise and Tsubaki act as decoys for Funatsu to catch. Reisuke poses as a lost child, luring Yomotsu to him where Reisuke explains the situation, prompting Yomotsu to side with Akise and helps expose Fuantsu. Reisuke is later seen with Tsubaki, the Seventh diary owners Marco Ikusaba and Ai Mikami, and Orin Miyashiro, aiding Akise to stop Muru Muru from erasing the alternate events of the survival game. However, she ultimately succeeds and Reisuke's death occurs anyway.

The Third World
Reisuke is reborn again when Yuno, Muru Muru, Yuki and Minene perform a time leap to the third world, appearing two years in the past. A two-year Reisuke is seen briefly, looking out of a window at the fight going on at the elementary school between Minene and Muru Muru. However, the fight alters history, saving Tsubaki's parents, and thus leading to Reisuke's parents being spared too. The final scenes show a happy Reisuke with his parents.