Yuno Gasai

Yuno Gasai is a young girl who is obsessed with Yukiteru Amano. She is the 2nd Diary holder.

Personality
Yuno's personality is an ambigous one, for the most part she is a sweet, femenine and sometimes shy girl when around Yuki. This masked her darker side that is of a ruthless, cold and calculating sociopath who has little if any problem in using others for her ends, that is her and Yuki's survival, and will resort to cruel and mostly violent methods that most of the time end in bloody deaths, of either the Diary User or any follower, effectively making her a Yandere.

While she's insane for most of the series, she was not always like that, and her brutal personality is a result of terrible circumstances surrounding her life, mostly the abuse she endured by her mother and the absence of her father, which finally ended with their deaths 2 years prior to the series. This was the beginning of her changes, as she later became quite lonely and sorrowful. It wasn't until she met Yuki who told her they would marry when they grew up, something at the time Yuki did not take seriously but for Yuno, it was the pillar of support she needed and from that point onwards, her obsession for Yuki grew to escalating proportions. Willing to harm those whom she believes will take Yuki away from here, such as friends, etc. This goes to the point that she considered resorting to violence if Yuki's mother ever opposed her, which luckily did not happen.

Later in the series as more background is given, her insanity is best understood. It is hinted that during the events of the 1st world, Yuno was not always the cold-murderer she was, as Yuki was seen protecting her, so she may have a more stable personality back then. Finally, after she wins the game and the cruel truth was revealed to her, that she and Yuki would never be together as she had wanted, she screams in despair. From this point onwards does her sanity turn into sorrow, with repeating the events of the game the only way she could ever be with Yuki, even if temporarily. For this means she will kill even Yuki, whom she still loves but cannot save, thus sparking conflict with herself. In the end her love proves superior and towards the end of the series, does her insanity and sorrow banish for good.

Plot Overview
There are currently 3 Yunos in the series: one from the orginal world, one from the second world (where most of the story takes place) and one from the 3rd world. The 1st is the most promenant in the story and does the most work. The 2nd was killed off by the 1st Yuno, and the 3rd Yuno's future was ultimately changed.

The First World
Deus's game was played up until Yukiteru and Yuno were left. They both decided to do a lovers suicide by taking pills that would kill them both. Yuno however secretly did not swallow the pills, resulting in her becoming God. She thought with her newfound power as God, could revive Yukiteru from the dead but soon realized it only brought back the body without the soul. Devastated, she and MuruMuru decided to travel back in time before the survival game started to be with Yuki again. This however created a parallel, second world. After Yuno arrived back in time, she killed the second world's Yuno and took her place in order to be with Yuki and go through the survival game again with him.

The Second World
The 1st Yuno has arrived into the 2nd world, at the point where her 2nd incarnation killed her parents. Deeming 2nd Yuno's unnecessary, she kills her off to take her place. This ends up being the mysterious 3rd skull Aru Akise discovers.

The Third World
Yuno once again intends to kill her 3rd incarnation in an attempt to repeat the game and be with the 3rd Yukiteru and travels back in time, creating a 3rd parallel world. However the 2nd world Yukiteru and the 9th followed her to try and stop her. Yuki arrived at Yuno's house before the 1st Yuno did and finds the 3rd world Yuno unconsious and locked in a cage. He frees her and decided to call the ambulance much to the 9th's annoyance after the 9th told Yuki to not get involved with the 3rd world since it isnt his world. Yuno arrives and then tries to kill her 3rd world self but Yuki and the 9th escaped with the 3rd Yuno. After that, the 9th parted ways to change the future of the other future diary users for the better. The ambulance came and so did Yuno's father. Worried that Yuno's mother did something to her again, the father approaches 1st Yuno but was stabbed by her because she still hated her parents.

First World Yuno soon caught up to Yuki right after he hid the 3rd Yuno. She tried to kill him and argued a little and eventually Yuno decided to lock Yuki up in a illusion world where Yuno didnt exist, Yuki's parents didn't die, and everything Yuki ever wished for was there because she couldn't bring herself to kill him. She then proceeds to kill her 3rd world self but the 3rd world father appears and defends the 3rd Yuno. Yuno's mother who saw her husband by chance rushes to help him. Yuno is astonished by this sight.

Yuki eventually broke free of the illusion world through will power and through the decision that he chose Yuno over this perfect world. After that, Yuki embraced Yuno, telling her he loved her, kill him and go back to the 2nd world and become god there. Instead of stabbing Yuki with her knife however, she stabbed herself instead. She told him again that she couldn't bring herself to kill him and told him to kiss her. The 1st world Yuno then dies in Yuki's arms. Because of Yuno's death, Yuki becomes god of the 2nd world and was pulled back by Murumuru.

Trivia

 * The characters of her last name mean "I" (我) and "wife" (妻), respectively.
 * Her first name is based on Juno.
 * In the first world she had won the game and become god.
 * She has two future diaries, the one from the 1st world and the one from the 2nd world.
 * Like Juno she is suspicous and jealous of anyone who tries to get close to Yukiteru.