It's not okay. Such content can make people uncomfortable and can have a negative impact on the overall image of the fan community. Fan fiction should focus on positive aspects like character development, new storylines within the boundaries of propriety, rather than delving into erotic themes.
Rather than erotic fan fiction, you can create a fan fiction about Enji's past. Explore his childhood, his family relationships, and how those experiences shaped him into the character he is today. You could also write a fan fiction that focuses on his career or his role in the fictional world, highlighting his achievements, his failures, and how he overcomes obstacles in his professional life.
His friends would probably take care of him. Midoriya would be very eager to help, using his kind-hearted nature. He would make sure Todoroki is fed and comfortable.
One common theme is redemption. Since Enji has made mistakes in the past, many fanfictions focus on him trying to redeem himself in Rei's eyes and in the eyes of their family. For example, he might take steps to be more understanding and less controlling.
One idea could be that all his friends at UA plan a surprise birthday party for him. They decorate the common room with his favorite colors, blue and red. Another plot could be Todoroki spending his birthday with his family, trying to reconcile with his father on this special day. Maybe he receives a heartfelt gift from his mother that has a deep emotional significance.