The Kerryūgan is a dōjutsukekkei genkai, which appears in certain individuals of the Chinoike Clan. The Kerryūgan is recognised by its reddish colour, giving a special appearance for the users of this dōjutsu, characterised as holders of "eyes as red as blood". The Kerryūgan confers genjutsu casting abilities. Its power earned it comparison to the Three Great Dōjutsu.
The Kerryūgan also gave the users the ability to manipulate the user's blood, or more accurately the iron in the blood, allowing the user to not only manipulate their blood, but any liquid with high iron concentration.
Ranmaru's Kekkei Genkai fits the description of the Kerryūgan. It is unknown, however, whether the two dōjutsu are one and the same.