Key Crystals are a set of four items found within the game, Bomberman Hero. They are first introduced at Planet Bomber's Area 1, within the Secret Room of Bomber Base. They take the shape of a transparent yellow diamond.
Sometimes, Bomberman will run across doors that are locked and have a four-sided star on them. It is within these types of levels Bomberman must find four of the Key Crystals in order to advance with the level. Some Key Crystals are in plain sight, while the others maybe hidden in not so obvious places. With the exception of the Secret Room, Key Crystals usually lead Bomberman to the end of the level. In short, it acts like a Card Key or Data Disk would do, only needing to collect 4 rather than one item.