How much should you tip in restaurants? or in hotels? or for any service in Japan?
Easy answer.
NOTHING. ZERO.NIL.NADA
Tipping is not part of Japanese commercial or social culture.
In a restaurant, if there are wait-staff, you may be presented with the bill/check at your table, but you are expected to pay it at the cash register (see picture) near the exit from the restaurant, not by leaving money on your table and just walking out. Hand the bill/check to the cashier, and place notes and coins, or credit-card, in that small tray on the counter in front of you.
(The bill/check sometimes does NOT include the 8% GST/VAT charge which is added onto the total, so have extra cash handy). If you pay in cash, you will be given exact cash change. NO TIP IS EXPECTED.
And DO NOT leave cash on your table as a tip to the wait-staff. There are stories which are quite believable, of staff chasing customers down the street to return to them the money they obviously accidently left on their table.
Japan Tourist Tips 