Saika Gasai

Saika Gasai (我妻 西果, Gasai Saika) is the adoptive mother of Yuno Gasai and the wife of Ushio Gasai. A minor character with major relevance, she serves as the direct cause of Yuno's descent into insanity.

Personality And Appearance
Saika was a woman with long brown hair, and orange eyes, wearing a dark green sleeveless dress. It is believed that Saika has bipolar disorder.

Although only seen briefly, Saika was a very strict and abusive mother towards Yuno. She felt lonely and neglected by her busy husband, and she took her frustrations out on Yuno by punishing harshly, locking her in a cage, feeding her little to no food, and calling her a bad daughter. In the anime Saika is seen to psychologically torture Yuno and then suddenly burst into tears and ask for forgiveness.

Yuno drugged her and her  husband  Ushio Gasai  then locked them in the same cage. Yuno believed that her mother would change if she suffered the same pain she had. At this moment Saika became much more hostile and maniacal, calling Yuno a devil and telling her she curses the day she was born.

During the end of the series, Saika in the Third World proves nonetheless to be a loving mother and wife who would put her own life on the line to save her family.

Behind the Scenes
It is known that years before the series timeline, Saika and Ushio decided to adopt Yuno. It is unclear whether Saika could not have children or suffered a miscarriage. Although initially a loving mother according to Yuno, she changed over time as she felt neglected by her husband who spent less and less time with his family as a result of his busy schedule. Saika would take her frustrations onto Yuno with a strict curfew and locking her up in a cage and feeding her little to no food at all as punishment. The anime, in particular, gives evidence that Saika highly regulated Yuno's life. She may have locked Yuno in the cage even if she obeyed, since she would call Yuno a bad daughter and measure the number of times she "talked back" as part of her regulations and punishment. Yuno endured this abuse for years knowing that her mother was suffering, but eventually she snapped and locked her parents in the same cage, with the same treatment, thinking the same treatment she suffered would make them loving parents again. This did not work, and her parents died from dehydration.

Though dead, she becomes as a major part of the series since Second World Yukiteru Amano  sees her remains when he chooses to open the door in Yuno's home. Her remains will become important in Aru Akise's investigation of Yuno. Finally, her character in the Third World will in part convince the First World Yuno to spare her Third World self and sacrifice herself instead of the Second World Yukiteru Amano.

The Final Battle
The Third World Saika is seen abusing her Third World daughter Yuno two years prior to the time period experienced in the Second World. Keigo Kurusu takes her in upon receiving reports. When Kurusu goes to the Sakurami Middle School where the final battle of the Second World's Survival Game is taking place, Saika rushes out of the car to look for her daughter despite Kurusu's warnings. She finds First World Yuno trying to kill her Third World self who was protected by her injured husband. She pleads with First World Yuno to take her life instead of her family's.

After the Second World's Survival Game ends, these incidents that nearly destroyed their family seem to have made united them as a family. Third World Yuno no longer suffers abuse and appears to have a fairly normal life. This suggests that in the Third World Saika received successful treatment.

Others
During when Minene and Yukiteru where traveling back in time to save the original Yuno, her father was outside the house before Yukiteru called an ambulance her father asked why she was taller. Yuno didn't hesitate and then stabbed him before he could say anything else.