So I have another suggestion, but with how much extra artwork it would entail, I would expect it to only be worked on after you've otherwise finished the game and go back to adjust things.
So I've seen the idea of fattening up other characters brought up, and I've realized that there is an interesting opportunity for that. On the morning after Legan's birthday party, if you go to Ziul's, it might be interesting if instead of volunteering for his project yourself, you could tell him that you know someone who would be more interested -- either Ian, Oken, or maybe Zac (all potentially depending on your relationship with them) -- and starting with the day afterward, they could gradually start to visibly gain weight. Maybe it could even have an effect on the "difficulty" of the sumo tournament.
Of course, just an idea to maybe look into later once you have more of the game done, but it might be good to make preparations for it if you go for sething like this.
And, a bit unrelated, was it intentional to drop Ian's weight down to 160 kg in the second sumo tournament, despite him being 180 in the first? It just seemed a bit odd to me.