Well, Syo Kurusu has an interesting back story. He was born with a natural inclination towards music. Growing up, he was exposed to different kinds of music which influenced his style. He entered the music scene with big ambitions. He had to overcome many obstacles such as finding his own musical identity among a sea of talented artists. His story is one of perseverance and the pursuit of musical excellence. He has worked with different producers and musicians, learning from each experience and gradually building his own reputation in the music community.
One common theme is the development of a romantic relationship. Usually, it starts from an initial encounter between the reader and Syo, and then gradually builds up to a deeper connection. Another theme could be Syo's journey as an idol and how the reader fits into that world, like supporting him through his performances and dealing with his idol - related challenges.
You can try searching on popular fanfiction websites like Archive of Our Own (AO3). There are a large number of fanfics there, and you can use the search function to specifically look for syo kurusu x reader fanfic. Another option is Fanfiction.net, though the tagging system might be a bit different, but it still has a good collection.
I think Christmas piano cartoons that have a heartwarming story behind the music tend to be well-liked. Maybe like a group of friends coming together to play piano for a charity event during Christmas. Also, ones with colorful and magical settings can attract a lot of viewers.
You could have them constantly trying and failing at diets or exercise routines in a hilarious way. Or maybe they have a love for food that leads to funny situations. Another option is to have other characters' reactions to them be funny, like being overly shocked or scared of their size.