Saika and Ushio Gasai

Saika and Ushio Gasai are the adaptive parents of Yuno Gasai and are the main reasons Yuno has driven into insanity in Mirai Nikki.

Storyline
Years before the series timeline, Ushio and Saika, decided to adopt Yuno as they were unable to have children of their own for unknown reasons. However, Ushio became very busy with his work and spent little time with his family, prompting a lonely and sorrowful Saika to become more and more strict towards Yuno, taking her frustration out on her. Although Yuno endured it thinking her family would be loving once more, at a certain point she had enough of it and trapped the two of them in the same cage she was abused, thinking that suffering the same would make them the loving parents she wanted them to be. He is presumed to have died out of starvation and/or dehydration, since he was denied proper feeding. The love he failed to give and his own death served as one of the main reasons for Yuno's insanity.

Even dead he serves a major importance within the series, as his death proves a major focus regarding Yuno, in particular, that Akise Aru would investigate Yuno, and that Yukiteru Amano would start doubting Yuno believing her to point of believing her to be a psychopath.