Japan is a truly beautiful and ancient country, and its symbols and iconography reflect its unique aesthetics and sense of the world. From the simple but vivid flag, to the deep connections to the beautiful, transient cherry blossom, Japanese symbols reflect an appreciation for a simple, clean, aesthetic that focuses on the transient more than the permanent.
The Japanese flag depicts a red disc, representing the rising sun, against a white background. This, of course, is a symbol of Japan's strong connection throughout the ages to the sun - even Japan's name for itself, "Nihon", translates to "origin of the sun". This connection is obviously partially due to the lack of any land anywhere near to the east of Japan, but there are also strong mythological ties, and the emperor of Japan was thought to be a descendent of the sun goddess Amaterasu. Given these connections, it is only understandable that Japan would choose the image of the rising sun for their flag. However, due to its connections to strong nationalism, flying the flag is somewhat out of fashion, and, sadly, this striking, beautiful design is now largely unseen.
The Three Sacred Treasures of Japan reflect the same sense of a Japanese connection to the sun and to Amaterasu. Never seen by public eyes, the three treasures - a mirror, a jewel, and a sword - are used to swear in each new Emperor. The myth surrounding them is that when Amaterasu locked herself in a cave because of her brother Susano-o, the other gods lured her out with the mirror and the jewels, knowing her reflection in them would make them more brilliant. The sword was an apology from Susano-o. Amaterasu then passed on the treasures to her human descendents. While elements of this are clearly legendary, the treasures remain critical to Japan and are a well-guarded secret. They also show up in popular culture in myth - in the popular Sailor Moon, for example, three of the warriors have a sword, a mirror, and a staff set with a jewel as their weapons.
The cherry blossom is one of the best known symbols of Japan. Japanese aesthetics and philosophy put a great deal of focus on the things which are transient and short-lived but beautiful, and cherry blossoms, with their short blooming period and their spectacular showers of petals as that period ends are a perfect symbol for this aesthetic. They thus have been commonly used as a representation of mortality, including as military propaganda, encouraging warriors to fight and fall like cherry blossoms. This focus on the transient might seem morbid, but in truth it also encourages an appreciation for beauty while it happens and for living life in a moment. A Japanese concept, mono no aware (meaning something like pathos), is often connected to this sentiment and to cherry blossoms in particular. Mono no aware encourages both appreciation for transient things and an understanding of their transience, heightening the beauty of things while they last and making the regret that follows part of their beauty.
Japanese symbolism is rich and deep, incorporating myth and reality, philosophy and beauty, into one unified whole.