Way back when, after the siege of Keppi’s castle, Otter saves Mabu’s live with a mechanical heart, but only if he makes a solemn promise. In the present, Reo reveals he’s a kappa too, once a vassal of Keppi’s along with Mabu. He shrink-wraps Keppi and demands the final dish of hope, but empathizes with Kazaki’s wish to save someone close to him, and so lets him tag along while he collects the other four dishes.
During the descent, Reo laughs at Kazuki’s earnest attempt to save his connection with Enta, and his jadedness is understandable; the Mabu they encounter is less his Mabu than ever; cold, distant, and in Reo’s words, nothing but a fake, half-baked doll. They descend further and find Dark Keppi, the half of Keppi created when he split his Shirikodama to escape capture by the Otters.
This otter demands the dishes, and also places Enta in “Enta’s World”, in which his desire—to be loved by Kazuki—is made real. But like Reo with the resurrected Mabu, it’s just not the same, and Enta escapes the fantasy. Reo has a key assist by shooting the head off the Otter and producing four of the five dishes needed, but just then Mabu jumps from a precipice and ends up transforming into a Zombie Kappa.
This means Reo has to be transformed by Keppi—like he and Mabu were in the old times—and go through the same (literal!) song and dance as Kazuki, Enta, and Toi. Even Miyano Mamoru’s casual singing voice is better than those of the other three, as he peers into Mabu’s Shirikodama and learns that in order to live and stay by Reo’s side, Mabu had to give up his connection with him.
That means when Mabu, who he only just freed from zombiehood, decides he can’t live on with that severed connection anymore. Pledging his everlasting love for Reo, his deal with Otter is broken, his mechanical heart stops, and he disappears. When the dust clears, Keppi creates a new fifth dish of hope (Kazuki broke one earlier) and Reo is beside himself with grief, unleashing it with his pistol in a destruction spree that ruins Asakusa’s bridges.
Then Reo forgets who Mabu ever was, and is then shot through the heart…by Toi, who has returned from the ferry. Kazuki thinks he’s changed his mind and come to rescue him and Enta, but Toi hesitates, wanting the five dishes to bring his brother back. Enta’s clock runs down to fifteen, ten, zero seconds…and Kazuki makes his wish, even at gunpoint.
When Enta wakes up, Toi admits he probably would have saved Enta too…but now he’s as full of grief and rage and desire as Reo was before he shot him. That attracts Otter, who looks to bring him under his influence, using the spectre of his older brother to lure him in. Once Chikai appears, whispering in his ear, Toi lets go of Kazuki’s hand and walks into the darkness of his own volition.
With Kazuki, Enta, Haruka, Mabu and Reo’s stories largely complete, the final episode will seek to close the book on Toi, one way or another, who has only had to live in a world without his brother for a few hours (maybe less), and is thus all too easily manipulated by Otter. We’ll see how Keppi and the Golden Duo fare against that negative influence, and maybe get back to being three normal soccer-loving kids.