Todoroki’s mom is in the hospital because Endeavor labeled her as mentally unstable. After she poured hot water on Todoroki’s face, Endeavor sent her to a hospital to house her for an indefinite period of time.
We learn more about Todoroki’s mother, Rei Todoroki, towards the end of season 4. Her words of encouragement were a main point of development for Todoroki during the Sports Festival arc of season 2. Rei has become a more prominent and frequently featured character in recent arcs.
She has apologized to Todoroki, profusely, many times. Todoroki forgives her and does not hold a grudge. He considers his father’s abuse on their family to have been the main source of stress in their home. Todoroki attempted to channel the hate he was expected to have for his mother, into his father.
Why Did Todoroki’s Mom Burn Him?
Todoroki’s mom burned him because he began to remind her too much of Endeavor. The constant abuse Endeavor put upon their family, both physically and emotionally, continually drained her over time. She took notice of Todoroki’s prominent left side, which represented Endeavor. Overwhelmed with emotions, she poured water from a steaming tea kettle over his head.
It’s up to Todoroki himself whether he forgives his mother or not.
As It Stands Now
As it stands now, Shoto Todoroki, alongside his two siblings Fuyumi and Natsuo, freely visit their mother at the hospital whenever they wish. Shoto began to secretly see his mother at first, but over time became more open to expressing his intentions and slowly convinced his siblings to visit their mother as well.
Todoroki’s mom is in the hospital because Endeavor labeled her insane, although he has seemingly attempted to patch things up with his family. He’s making attempts to visit Todoroki’s mother in the hospital and connect further with his kids.