A bicycle is too big for any bag, so it counts as oversized garbage. It has one extra step a futon does not: the registration.
Most bikes in Japan carry a 防犯登録 (crime-prevention registration) sticker tied to your name. Before you scrap the bike, cancel that registration so it does not stay linked to you. Bring the bike and your ID to a bicycle shop or a police box (交番) and ask to cancel. It takes a few minutes and a small fee.
With the registration cleared, the bike follows the normal sodai gomi path:
A working bike does not have to be trash. Recycle shops, flea-market apps, and some bike shops will take or buy a usable bicycle. Hand it over with the registration cleared, so the next owner can register it under their own name.
Abandoned bikes get tagged and removed by the city, but that is not a disposal method. If the bike is yours, clear the registration and book the pickup.
Not sure where to start? Gomi Guide walks you through the booking and fee for your area.
Sort the bike booking in the app Gomi Guide walks you through the bike's pickup and fee for your area. Free on the App Store.