The traditional set
A classic Japanese breakfast (wafuu asagohan) typically includes steamed rice, miso soup, grilled fish, pickled vegetables (tsukemono), a sheet of dried seaweed (nori), and often a raw egg meant to be mixed into the hot rice — a combination that reads as a full savoury meal rather than a lighter Western-style start to the day.
What hotels actually serve
Business hotels and larger properties increasingly offer buffet breakfasts covering both Japanese and Western styles side by side — toast, eggs and coffee alongside rice, miso soup and grilled fish — letting guests mix and match rather than commit to one style. Smaller guesthouses and ryokan are more likely to serve a fixed traditional set.
The convenience store alternative
For an easy, cheap breakfast on the go, konbini cover both bases well: onigiri and miso soup cups for something closer to the traditional style, or sandwiches and coffee for something closer to Western habits. It's a reliable fallback on early travel mornings when a sit-down breakfast doesn't fit the schedule.