While rinsing off their equipment from their last dive, Futaba Ooki, Hikari Kohinata and Ai Ninomiya discuss what happened during the navigational training. Ai scolds Hikari for leaving her buddy alone during a dive, because diving buddies should never stray away from one another on a dive, but Hikari insists she was always nearby. Futaba asks why Ai and her brother aren't cleaning their equipment, and Ai explains that she and Makoto are planning to do some night diving once the sun goes down. Hikari asks Futaba if night diving is something she'd like to try, but she immediately declines at the thought of diving in the dark and not being able to see. Futaba and Hikari go off to shower, and then meet Ai and Makoto back on the beach to wave them off as they go on their dive.
While they stand and watch the Ninomiyas preparing, Futaba starts to overthink how scary it must be to be surrounded by the darkness while underwater, but accidentally says her thoughts outloud. Hikari responds and tells her that not being able to see in front of you is half the fun. Going into herself, Futaba becomes depressed because despite being on such a high and feeling so brave after her navigational training she's now curling back up into a ball inside herself again about something that everyone else thinks should be enjoyable - she keeps finding herself looking back instead of looking forward.
Ai comes over and passes Futaba a glow stick, something she's never seen in real life before. She snaps it and is surprised by how bright it is. Ai tells Futaba that they attach glow sticks to their tanks so that other divers can see where they are even in the dark. Makoto then shows Futaba a high powered underwater diving torch which is incredibly bright.
Futaba and Hikari wave off the Ninomiyas, and before they know it, the ocean is full of night divers each carrying their own lights and looking like an ocean of stars. Hikari explains that during the day, the light from the sun refracts into the sea and everything underwater appears blue, but when you dive at night with close range lights you are able to see the true colours of fish and coral. Futaba wonders to herself if one day she'll be brave enough to not look back into the darkness as long as she has a bright light and Hikari beside her. Hikari turns around and asks her if she'd like to try night diving with her next time. This time Futaba agrees.