Afternoon tea is getting popular in Japan, especially in metropolitan area. Afternoon teas are enjoyed at luxurious hotels, mostly 5 stars hotels.
It depends on the hotel, but you can enjoy savory foods such as sandwiches and sweet foods such as scones, cakes and other sweets. Beverage can be chosen from tea and coffee. Most places offer unlimited consumption of beverage in case the afternoon tea has time limit.
It is better to make a table reservation in advance and check carefully the price. Tipping is not necessary in Japan but these luxury hotels and restaurants charge automatically service charge which is 10-15% of the bill.