Maybe there could be a new character introduced, like a wise old man or woman who has knowledge about such strange transformations. This character could guide Touma through his experiences as a child and help him understand the meaning behind this change. Additionally, any potential villains in the story would also be important characters as they could pose a threat to child Touma.
A common theme is redemption. Othinus, having had a complex past, often goes through a process of redemption in these fanfics, with Touma playing a significant role in it.
Perhaps in the fanfiction, when Touma turns into a child, he discovers a new side of the world he didn't notice before. As a child, he has a different perspective. Maybe he befriends other children who are in some sort of magical or dangerous situation, and his child form has unique powers to help them. The story could be about him growing and learning while in this child form.
Love and acceptance is also a big theme. They come from different backgrounds, with Misaka being part of the Academy City's esper system and Touma being an ordinary boy in some ways but with extraordinary powers. So, the fanfictions often explore how they come to accept and love each other despite these differences. And of course, there's the theme of protection. Touma often finds himself protecting Misaka, and she in turn wants to protect him, which creates a nice back - and - forth in the stories.
There are fanfics where the author delves into the emotional bond between Touma and Othinus. These often include detailed descriptions of their conversations and how they gradually come to understand each other on a deeper level. Some might also involve adventures that they go on together, strengthening their relationship along the way.
One great Misaka Mikoto x Touma fanfiction is 'A Certain Encounter'. It beautifully depicts their relationship with well - written dialogue and interesting plot twists. The author does a great job of getting into the characters' heads and showing their complex feelings for each other.
A standout fanfic might have an exciting new power or ability for Touma, or maybe it explores his relationships in a fresh way. Maybe it even creates an entirely new adventure for him in a different setting.