Bountos - Non-Soul Reapers - Zanpakutō Spirits - Ryūjin Jakka

Ryūjin Jakka is a Zanpakutō owned by Genryūsai Shigekuni Yamamoto. It is the primary plot element in the anime's "Zanpakutō Rebellion" arc, sought by Muramasa to use for his own purposes. Unlike the other Zanpakutō spirits, Ryūjin Jakka doesn't have a solid form and is mostly seen as intensely hot flames. When Muramasa freed Ryūjin Jakka from his Zanpakutō form, it prevented the other Soul Reapers from following Muramasa until Tōshirō Hitsugaya and Hyōrinmaru arrive and freeze Ryūjin Jakka's flames with their Bankai, allowing Ichigo to escape. The others remain inside the flames. Yamamoto decides that it is time to punish his rebellious Zanpakutō. The outcome was not shown.

Read more about this topic:  Bountos, Non-Soul Reapers, Zanpakutō Spirits