Japan is in its storm season right now, August to October. Most trips are unaffected, but a storm reroutes flights and closes beaches at a day's notice — the packing consequence is a buffer day and a charged power bank, not different clothes.
Going in March
Nothing seasonal is running in March.
Packing for Japan?
Build a packing plan around the season you are actually travelling in.
Seasonal ranges are typical, not guarantees — a monsoon can arrive early and a dry season can break. Check the forecast before you seal the bag.