Ranmaru's Kekkei Genkai

Ranmaru possessed a dōjutsu kekkei genkai which, when activated, causes his eyes to glow red in colour. It grants him abilities such as penetrative vision as well as the ability to hinder other dōjutsu such as the Byakugan which his own dōjutsu has been likened to.

Overview
Ranmaru's technique abilities include penetrating vision, disruption of eye-based kekkei genkai, and a unique chakra particle extension.

He has the ability to use his vision abilities to penetrate the walls of his small shack and view the outside world and perform genjutsu that can fool even the all-seeing Byakugan. This ability does not appear to have the range of the Byakugan, but it actually has the ability to counter that Hyūga trait. Ranmaru's vision also lets him locate and track others by sensing chakra, picking up chakra from long distances, and noticing changes in an individual's chakra. It is also able to sense how many individuals are present.

Ranmaru's vision has heightened perception and analytical powers like the Sharingan, meaning Ranmaru can comprehend any details he sees to predict the opponent's next move. He mainly contributed this ability to helping Raiga become formidable in battle, and may have helped him become one of the Seven Ninja Swordsmen of the Mist. He can also see one's life force, allowing him to determine that Raiga, who had recently fallen in battle, was still alive. He was also able to transfer part of his own life force to Raiga.