Ushio Gasai (我妻 潮, Gasai Ushio) is the adoptive father of Yuno Gasai and the husband of Saika Gasai. A minor character with major importance, he serves as an indirect cause for Yuno's descent into insanity.
Little is known of Ushio due to his brief appearance, although when first mentioned he was described as an elitist and (once) abusive parent towards Yuno.
In stark contrast to this, however, Ushio was shown to be in fact a loving father to Yuno, and a seemingly good husband too, but otherwise restricted in both of these duties because of his busy schedule as a bank owner. It is briefly shown that Ushio was hostile towards Yuno when he was trapped inside a cage himself, although this is made more obvious in the anime. However, his anger seemed to stem from not understanding why Yuno imprisoned him, as he was not aware of Saika's abuse toward her. In the manga, it is Saika who furiously yells at Yuno.
Behind the Scenes
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 be a psychopath.
The Final Battle
He is briefly seen in the past receiving a call from the hospital after Yuki had decided to change the future and save the third Yuno, given the reports of Saika's abuse. He encounters the first Yuno and asks her if she is alright. While in the manga it is unknown how she evades him, in the anime, Yuno stabbed her father in a fit of rage and later goes after Yuki and her third self. After trapping Yuki in her illusion world, Yuno prepares to kill her third self, but Ushio timely arrives and is stabbed in the arm instead, with Saika pleading to the first Yuno to spare their family.
Finally after the Survival Game ends, it is seen that the incident that had put their family in danger made them a much happier and united family as the third Yuno is no longer abused and lives a fairly normal life. Given that he survived, it is also hinted that the previously in bankrupt Gasai Bank is either growing or stable.