Should I bring a big suitcase?

Avoid it. Japanese train stations are often crowded and full of stairs. A medium-sized checked bag or a large carry-on is the maximum you should bring to navigate subways easily.

Do I need formal wear?

Generally, no. Japan is quite casual for tourists. Unless you are attending a high-end dinner or a business meeting, smart casual (jeans, clean shirts/blouses) is perfectly acceptable everywhere.

How to Pack for Japan’s Seasonal Climate

Japan’s distinct four seasons mean you must pack for extreme variety: lightweight, breathable layers for summer humidity and a heavy, insulated coat for winter. Always prioritize slip-on shoes and a high-quality umbrella, as you will be doing significant walking and dealing with unpredictable rain.

Assess the season. March-May (Spring) requires light layers and a medium jacket. June-August (Summer) demands moisture-wicking fabrics and light linen. September-November (Autumn) is similar to spring with slightly heavier knits. December-February (Winter) requires a thermal base layer, wool sweater, and a windproof down jacket.
Follow the 'easy-on, easy-off' rule. You will take your shoes off dozens of times a day in temples, traditional restaurants, and guesthouses. Pack slip-on sneakers or loafers, never lace-up boots that take five minutes to tie.
Use a modular packing system. Use packing cubes to separate your clean clothes from your worn ones, as laundry facilities (coin laundromats) are everywhere in Japan, meaning you only need to pack for 7 days regardless of trip length.
Prepare for the rain. Regardless of the season, Japan is prone to sudden downpours. Pack a packable rain shell or a light, high-quality travel umbrella. If you forget, buy a cheap, clear plastic umbrella at any 'konbini' (convenience store).

Should I bring a big suitcase?: Avoid it. Japanese train stations are often crowded and full of stairs. A medium-sized checked bag or a large carry-on is the maximum you should bring to navigate subways easily.
Do I need formal wear?: Generally, no. Japan is quite casual for tourists. Unless you are attending a high-end dinner or a business meeting, smart casual (jeans, clean shirts/blouses) is perfectly acceptable everywhere.