Gathering Light (集う光, Tsudou Hikari) is the sixth episode of Koutetsujou no Kabaneri.
The Black Smoke is revealed to be a colony of Kabane fused together. Having no choice, the Koutetsujou retreats to the train station workshop and seal the door. Ikoma finds Mumei trapped under rubble and tries to get her out. Meanwhile on Koutetsujou the committee is discussing their options of escaping and whatever they leave the Kabaneri behind or not.
Ikoma fails to free Mumei and as Kabanes approach, he decides to leave them away and fight them, killing as many as he can. As Mumei loses and regains her consciousness, he recalls her past and how her mother died. Kibito, Kurusu and some others them come and clear the rubble freeing Mumei. Mumei then rushes to find Ikoma, who is badly injured and they return to Koutetsujou together. While the Black Smoke is distracted and takes in Kabane bodies, Mumei explains its Fused Colony. Sukari had noticed earlier a Type 48 Cannon and Koutetsujou had went and taken it. Mumei explains that a single Kabane had become the Fused Colony heart and that they need to expose it and she will kill it. Meanwhile, Ikoma had clears the debris from the tracks.
As Koutetsujou go, the Fused Colony goes after them. Takumi fires the cannon a bit early and that only causes Kabanes to land on the train. Ikoma, Kurusu and the bushi take care of the Kabane. As the Fused Colony approaches the front cars, Takumi sees an opportunity and shots the cannon again, hitting the heart and revealing it. Mumei immediately jumps to take out the heart, to her surprise, the heart was a fellow Kabaneri comrade turned Kabane. As she takes it out, the Fused Colony disbands and Koutetsujou manages to leave the station.
- The Kabane Katana was first used in this episode.