Main character will be reborn in Zaun (arcane League of Legends) with a scientist system. (Kind of works like a template system)
Limitations for main character:
1. System can only give knowledge nothing else and takes time to truly understand that knowledge.
2. MC will have no knowledge of the world he is reborn in.
3. System limits you can get for a template so not to get someone op like Rick Sanchez or Lex Luthor. (you could make a rank so you need to be like 5 star to be able to get them for a template)
for the plot:
1. Don't stop Milo and Claggor death as it's needed for the plot (kinda like Batman's parents dying)
Ideas for main character:
Age: 3 years younger then jinx (gives you a good excuse for not saving Milo and Claggor)