In summer, it is good to have loose fitting clothing and some light trousers. For men, white short sleeve shirts are very common in summer. Bring some shorts for days off and sports activities. For winter, pack long-johns, leggings, and other clothing that can be layered underneath your clothing. The school classrooms are heated but the halls are not so you need warm clothes in school as well as outside school.
Footwear is a classic problem in Japan.
If you have large feet, you might want to bring a pair of slippers as well. You will need separate indoor shoes for school. Try to find something you can slip on and off in a hurry. Hiking boots or supportive footwear are real useful in Fukui. Formal wear , don't leave home without it.