On the other hand, if he drinks coffee regularly, he could also become more focused and serious. The caffeine in coffee might help him concentrate better on his ninja duties. He might start planning his missions more carefully and thinking things through more thoroughly instead of just charging in headfirst like he usually does.
It could also make him a bit more irritable. If he doesn't get his regular dose of coffee, he might be short - tempered. And he might start to rely too much on coffee to get through his day, which could lead to some self - discovery when he realizes he's become a bit too dependent on it. He could then try to cut back and learn to find his natural energy again.