It's hard to say it's a widely 'popular' genre in the traditional sense. While there may be some fans who explore such themes in fanfiction, it's not something that represents the mainstream of Splatoon fan works. The Splatoon series is mainly known for its unique gameplay and colorful characters, and most fanfiction focuses on things like character relationships, adventures in the Splatoon world, and interpretations of the game's lore. However, in the vast realm of fan-created content, there will always be a small subset of more niche or out - of - the - ordinary concepts like this.
The uniqueness of their relationship. Tam and Sheldon are both very different characters. Sheldon is extremely intelligent but socially awkward, while Tam has his own set of qualities. Fanfictions that explore how they interact and complement each other are special. For example, Tam could help Sheldon in social situations that he struggles with, like understanding group dynamics at school.
Perhaps an intelligent and patient psychologist. She could help Sheldon understand his emotions better. Given Sheldon's complex personality, she would need to be very understanding and be able to handle his idiosyncrasies. This type of girlfriend could also introduce Sheldon to the world of human emotions in a more systematic way.
One great Young Sheldon Tam and Sheldon fanfiction could be one where Tam helps Sheldon with a difficult science project at school. Tam might bring in some unique ideas from his own background that Sheldon hadn't considered. Another could be a story about their friendship growing over shared interests in comic books, despite their different personalities.