Boulders are a Sentry Beast appearing in Okamiden. There are four types, three of them having control over a specific elemental power. They are stone spheres that roll around the area trying to bump into Chibiterasu or his partner to hurt them. They all have an eye engraved into their body. They mainly serve as a power sourch to allow Chibiterasu to use his elemental based Brush Techniques. They appear regularly in Divine Springs, allowing Chibiterasu to open the Treasure Chests there.
They attack out of the rage they feel over the fact they cannot walk.
 Death Boulder
These are the most basic type of boulder and the first type Chibiterasu meets. They do not have control over any type of element. They are first encountered in The Cave of Nagi.
"A normal boulder until it was possessed by evil and became a demon minion. Its movements are choppy and erratic at best. Jealous of those who can walk without impediment, it will attack on sight."
 Flame Boulder
"These creatures were caught in a volcanic eruption and filled with rage. The pain of being engulfed in flames lead to erratic movements. In an effort to end their torment, they lash out at others. Their flames will set anyone on fire who comes in contact with them."
 Spark Boulder
"Humans who no longer appreiciate the bounty of the land, will feel the stormy rage of 1,000 bolts of demonic lightening! These hunks of electrically charged dried lava will attck indiscriminately and give their victims the shock of their lives."
 Ice Boulder
"Humans who no longer appreciate the beauty of the land, will feel the cold rage that resides within these creatures. They can freeze a human to the core by brushing against them"