Ai Mikami

Ai Ikusaba (美神 愛, Ikusaba Ai), (née Mikami), is one of the Seventh diary owners, which is shared with her boyfriend/husband Marco Ikusaba. Devoted to Ikusaba, Ai and Marco share the "Exchange Diary", which the couple uses to keep an eye on each other at all times. They wish to become Gods so they can be together for all eternity.

Appearance & Personality
Ai is a beautiful woman, dark blue-haired, and purple-eyed, and the long-time lover/wife of Marco Ikusaba. From a young age, she loved Marco after he befriended her and gave her a family after she was abandoned by her parents as a child. She is very devoted to him, and together they form a strong battle couple. Ai is implied to be a flirtatious person, since the Apprentice Diary she gained, the "Flirting Diary", involved identifying the men she would flirt with. She seems to be at peace with Marco's constant fights.

Despite participating in the survival game, Ai and Marco have morals. Ai takes sympathy towards Tsubaki Kasugano, the Sixth diary owner, although she expresses the knowledge that sooner or later that Tsubaki would turn into an enemy if she and Orin Miyashiro had helped her with her troubles. Ai and Marco also refuse to take a life that they do not plan to, treating the wounds of Hinata Hino and Mao Nonosaka who Ai had injured with her knives.

Diary & Abilities
Marco and Ai share the Exchange Diary, which appears as two mobile phones. The diaries allow Marco and Ai to predict each other's movements and can protect each other when in a fight. If one of the diaries is destroyed, the other owner remains alive. The main advantage of this diary is that depending on how it is used it can predict her own future or Marco's. Using the latter method she can predict anything related to Marco and protect him and vice-versa, creating a fearsome combination. The main weakness of this method, however, is that if the two are separated, then they are obviously unprotected.

She was also an owner of an Apprentice Diary known as the Flirting Diary. This allowed her to know with which male she's going to flirt next. The rather only use this diary has is to track foes, so as long as they are of the male gender, but nonetheless useless if they are female and for the game's sake if said males are not participants. Like all of the Apprentice Diaries, hers depends on her connection to The Eighth's diary. If there is jamming then it is rendered useless. And also she won't die if this diary is destroyed because it is an Apprentice Diary.

She's also a skilled knife thrower. She keeps a collection of throwing knives in her jacket and can throw them with pinpoint accuracy. However, she only has so many and is bamboozled when Yuno Gasai is able to deflect them all. Nonetheless, during the events of Future Diary: Mosaic, her accuracy is so precise that she's one of the "three" main reasons why the Sakurami Beauty Contest (one of the trials) is boring, being always the victor in throwing.

Although not being a brawler like Marco, she does seem to have above average skills of her own, as she could restrain Yuno in a proper manner (that is putting her on the floor and restraining her from above) as well as fast reflexes, being able to avoid a dart thrown by Yukiteru, albeit with warning from Marco.

She also seems to be knowledgeable in other things like infiltration, first aid and parachutes.

Background
Fourteen years ago, Ai was abandoned by her parents at the Sakurami Tower and was told to wait for them to return. By sunset, Ai realized her parents had gone and cursed the day as being the worst of her life. It was at this point that Marco approached her for the first time, having observed her for most of the day. He told her that if that day was her worst day, then the next day would be better. Marco invites Ai to come live with him in Mother's Village, the orphanage of Kamado Ueshita, who would become the Eighth diary owner. Ai accepted.

In high school, Ai started her first year following Marco around, having grown quite attached to him.

Marco objected to her following him around all the time, but he eventually relents. The two grow close, and were implied to be dating despite Marco being a street fighter. The two eventually revisited the Sakurami Tower, Ai revealing she had her own diary based around Marco, which he suggested should focus on something other than him. The two visit the tower's chapel, Ai revealing she wants to marry Marco in the chapel.

Later, Ai finds a letter requesting a meeting in an abandoned factory. Assuming Marco sent it, Ai goes to the factory only to be ambushed and sexually assaulted by four boys. Marco arrives, angrily beating the boys and kills one of them when they draw a knife. Returning to the tower, Marco nearly kills himself with the knife but is stopped by Ai, who promises to emotionally support when he is in pain. Both declare their love for one another, kissing atop of the tower. However, the highschool event was a filler for the anime as in the manga no such events occurred and it was only shown that Ai and Marco bonded from their first meeting in the tower.

The Cult of The Sixth
Ai debuts early in the story alongside Orin Miyashiro, working undercover at the Omekata temple for Kamado to observe the other diary owners. The duo act as attendants for Tsubaki Kasugano, but they are by no means loyal, planting a bomb inside a futon which causes a fire in Tsubaki's confinement room. The attempt on Tsubaki's life is thwarted by Yukiteru Amano, Yuno Gasai and Keigo Kurusu.

Ai and Orin later tend to Tsubaki's wounds after her hand was chopped off by the enraged Yuno, Ai asking Tsubaki to stay still, although Tsubaki claims she has been in worse pain, hinting to her past. Ai is present when Yukiteru runs in and destroys Tsubaki's Future Diary. Presumably, Ai and Orin were able to escape police custody and returned to Marco and Kamado.

The Seventh's Battle of Love
Marco and Ai were sent by Kamado to intercept Yukiteru and Yuno, unaware of Yukiteru's kidnapping by Yuno. Marco, Ai, and Ta-kun, one of Kamado's orphans, pass by Yukiteru and his friends in a convertible. Ai shows disappointment at missing the chance to meet Yukiteru.

Several days later, Yukiteru plans to paralyze Kamado's Future Diary by jamming a nearby phone communications tower to disable the Apprentice Diaries. Marco and Ai break into Ouji Kosaka's house to confront Yukiteru and the recent arrival of Yuno. Ai displays her knife throwing skills by wounding Hinata Hino and Mao Nonosaka, Yukiteru and Yuno escaping into a room through a trap door. Ai and Marco confront them, but their Apprentice Diaries are disabled when Kosaka and Aru Akise jam the tower.

However, Ai and Marco are hardly surprised, revealing that they are the Seventh diary owners. The two immediately challenge Yukiteru and Yuno to a fight, Ai throwing knives which Yuno blocks. Ai is gobsmacked by Yuno's remarkable aiming skills and throws all of the knives she has, Yuno blocking each one, inspired after Yukiteru praised her. With no other option, Marco and Ai resorted to their Plan B, namely to retreat. Ta-kun set the house on fire, Marco and Ai taking Hinata and Mao outside to treat them, unwilling to have innocent lives lost in their fight.

The two head back inside the burning house to confront Yukiteru and Yuno again. Ai and Yuno directly confront each other, Ai horrified by Yuno's concept of earning someone's love. She manages to put up a fight, but trips on a rug, leaving an opening for Yuno. Marco runs through the flames, blocking Yuno's attack and is injured, but the lovers are able to defeat Yuno, and Yukiteru shortly afterward, stealing their Future Diaries and leaving.

Ai learns from her diary that Marco will eventually buy her an engagement ring and is thrilled that Marco will eventually propose to her, much to Marco's surprise. Marco contacts Yuno, inviting her to attempt to rescue hers and Yukiteru's diaries, asking her, Yukiteru and Kurou Amano to come to the Sakurami Tower.

Upon Yukiteru, Yuno and Kurou's arrival, Marco and Ai have already married. Kurou asks Marco to hand over their diaries, but Marco promptly beats Kurou before fighting Yukiteru again. Kurou grabs Yukiteru's diary and seemingly destroys it. However, Yuno quickly realizes the diary destroyed was a replica, and seizes the real diaries inside Ai's bouquet. Ta-kun begins to demolish the tower, encouraging Ai and Marco to escape to the top floor where they plan to parachute their way to safety, taking Kurou with them.

Yukiteru and Yuno rush to the top floor, Marco and Ai arriving shortly afterward to find Yuno alone. Yukiteru talks through loudspeakers, explaining he is hiding out but aiding Yuno from afar. Enraged, Marco fights Yuno and leaves her in Ai's hold, charging up to the control room to confront Yukiteru only to find him missing. Downstairs, Yukiteru reveals he was hiding in the observation room all along, and tries to take out Ai's diary with a throwing dart. Marco runs back in, telling Ai to dodge it. The dart misses Ai by inches, but allows Yuno to move, and she slashes Ai's throat with a knife.

The tower's roof collapses, trapping Yukiteru, Yuno and Ai beneath a layer of rubble. Ai mocks Yukiteru and Yuno for failing to kill Marco, who she believes will escape alone. Yuno holds her at knifepoint, but Marco shouts out, refusing to leave Ai behind and he begins lifting a piece of rubble to save Ai. Marco encourages Yukiteru to help out, chastising him and Yuno for their selfish actions. Marco manages to raise the rubble enough but reveals he has been impaled by a metal rod. Yukiteru convinces Yuno to help out, and they manage to lift the rubble and help remove Ai.

However, by the time they do, Ai has died from blood loss. Marco cradles her in his arms and gives the last parachute to Yukiteru and Yuno to escape. Marco dies with Ai as the tower collapses.

The Final Battle
Ai and Marco appear in the third parallel world created when Yuno, Muru Muru, Yukiteru and Minene Uryu perform a time leap two years into the past. They are seen with Kamado at her Mother's Village orphanage as John Bacchus calls her regarding the future. In the anime, she is seen sleeping with Marco while she hears the commotion at Sakurami Middle School.

Two years later, Marco and Ai are seen walking together amongst a street of people. It is shown that Ai is clearly pregnant. In the anime, Ai chats with Marco in a cafe, telling him he must work harder in the future.

Future Diary: Paradox
In Future Diary: Paradox, Aru Akise and Muru Muru are forced to stand in for Yukiteru and Yuno after Muru Muru messes up the future by killing Yuno. Akise decides to alter the game's future by saving Tsubaki from death, convincing Ai and Orin to help him by disguising Ai as Tsubaki as a distraction so he can escape with the real one. Ai is found out by Funatsu and is shown being taken away by Omekata followers. She is later seen after Funatsu is exposed, safe and sound. When Muru Muru plans to rewind the game to alter her mistakes, Ai, Marco, Orin, Tsubaki and Reisuke Houjou come to Akise's aid to stop her. Marco and Ai fight Muru Muru and the brainwashed Yukiteru, but Muru Muru succeeds in her task and erases Paradox's events from history.

Trivia

 * Ai is named after Venus, the Roman goddess of love and beauty. Her surname 美神 means 'beauty god', while her given name 愛 means 'love'. Her husband Marco's name relates to Mars, and in Roman mythology, the two (Mars and Venus) were very in love with each other. Their relationship is obviously a reference to this.
 * Marco and Ai's character theme song is "7th Heaven" by Yousei Matsui and Choucho.