There are several things at Japanese airports which are not common at airports in Europe.
At first, you do not have to show your ID upon check in. ID is not required at gate either. The second thing is that you have to enter your age upon booking your flight. Therefore you can use your schoolmate's boarding pass but you cannot use a boarding pass of a passenger who has the same name as you but the ages are different.
Another thing is that you do not have to throw away a bottle of water or tea upon security check. If the bottle is not opened, no action required. In case the bottle is open, the security staff will check the bottle(liquid) using a special device.
Then, the boarding information slip. This slip is issued when you scan your boarding card at the security check. All necessary information are mentioned on the slip including the gate number. However, this slip is not a substitute for the boarding pass. Therefore you need to scan your boarding pass at the gate again. By the way, no one will check this slip later or you have to pass it after reaching the destination. Which means the reason to issue this slip is unknown.