Keep the beach clean!
Although beaches do not have many strict rules, one that is implied is to keep the beach clean. Similar to other manners, Japanese tend to think about other people who may use the space later. Therefore it is important to not leave trash around when you leave. This may be difficult, because there are not as many garbage cans around the beach. If this is the case, put it in a plastic bag and carry the plastic bag around until you find one. There are usually garbage cans near the eating and resting areas of the beach!