How can I make him better?

I just recently got his signature weapon, is there any other way that I can make him better? (Minus levelling up his talents cuz I am, it’s just really slow) Also if anyone could tell me what characters go well with him? I plan to get Furina but I’m not sure about who else would be beneficial.

I just recently got his signature weapon, is there any other way that I can make him better? (Minus levelling up his talents cuz I am, it’s just really slow) Also if anyone could tell me what characters go well with him? I plan to get Furina but I’m not sure about who else would be beneficial.