The Ketsuryūgan (血龍眼, Literally meaning: Blood Dragon Eye) is a dōjutsukekkei genkai, which appears in certain individuals of the Chinoike clan. The Ketsuryūgan 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". Its power earned it comparison to the Three Great Dōjutsu.
The Ketsuryūgan confers genjutsu casting abilities, either by making physical skin contact with the target or meeting each other's gaze. The Ketsuryūgan also gave the users the ability to manipulate iron, or more accurately, any liquid with a high iron concentration. As such, fitting with its moniker, the Ketsuryūgan can manipulate the blood within a living target, whether if be themselves or another being.
When written as 血流, ketsuryū means "blood flow".
The Ketsuryūgan's description in both appearance and genjutsu might is similar to the Kekkei Genkai of Ranmaru from the Kurosuki Family Removal Mission filler arc. It is unknown whether the two dōjutsu are one and the same. However, the anime's depiction of both dōjutsu gave clear difference in design between them.