A young girl, Sui, is infected with a mushi strain that inhabits the eyes (yes, this is an Eye Scream episode), causing the slightest bit of light to bring her intense pain. Her family leaves her in the care of relatives with a solid storage shed, and the son, Biki, plays with her and keeps “the light of her heart” going. Unfortunately, he too contracts the infection, and it’s up to Gingko’s arrival to salvage the situation.
Unlike the rest of the series, this is very definitely an early Mushi-shi episode, set when the time hadn’t yet been tied to an older Japan; anachronisms like a syringe show up, and in the original manga, Biki wore a t-shirt instead of a kimono. And this isn’t the most compelling episode of the series either, although there’s no less heartbreak when her relatives finally take Biki away from Sui. Gingko’s arrival is much later in the story, albeit his ability to rescue the girl’s sight (somewhat) is amazing in a Hayao Miyazaki kind of way:
The second-most striking element in this episode is its addition of more details about the underground river of light/life, and the fact that Gingko is always present mystically at it. He can be perceived by the right people (such as those infected by eye mushi), and he can see them. It’s a remote and dangerous connection, since staring at the light for too long is exactly what causes Sui’s original eyeballs to be devoured.
And the most striking is an allusion to Gingko’s backstory: his missing eye is full of darkness in a similar manner to Sui’s before he gives her a new eye (fashioned from his glass eye). Was it caused by staring at that river? It’s certainly a mushi-related injury.
Only time will tell us what happened.