While I could absolutely keep watching just Kou, Nazuna, and the night for ten or eleven more episodes, the introduction of Asai Akira doesn’t ruin the vibes. In fact, she brings a unique dynamic: Kou’s only human friend, something he didn’t think he had in her. When he placed the blue watch on the mailboxes, he didn’t mean to place it right above Akira’s, but that’s how she took it.
When Kou was an aloof kid off on his own in the playground, only Akira went to him to see what he was up to. When he said he was fine not joining the others, she joined him instead, and declared them friends. He didn’t object, but he probably forgot that exchange that Akira dutifully maintained. She still considers him a friend, and is glad he’s doing okay.
So Kou begins leaving ever-so-early from his nightly visits to Nazuna’s for some bed-lying and blood-sucking so he can meet up with Akira (who is an early bird to his night owl). Nazuna jokes that he’s going off to see another woman, and immediately senses from his expression that she’d accidentally nailed it. That said, Kou admits in voiceover that he and Akira don’t do much other than exchange inoffensive small talk.
On one such occasion in the park, he asks if Akira is having fun. She puts the question to him, and he says he isn’t not having fun, so she replies that she is. Just as Kou, extremely inexperienced in such things, starts wondering if Akira likes him, Nazuna menacingly emerges from the shadows only to give Kou a friendly pat on the shoulder and congratulate him for doing “hanky-panky”.
She tells Akira her and Kou’s relationship is “purely physical”, and while Akira’s mention of romance (upon hearing Kou call her “Nazuna-chan) once again makes Nazuna blush, she shakes that off by basically marking her territory, sucking Kou’s neck right in front of Akira and announcing she’s a vampire.
At a 24-hour café, the three sit, and Akira tries to grasp the situation. She asks Kou if he’s skipping out on school because of Nazuna. While she may kind of be the reason now, she wasn’t the original reason, which was that he simply couldn’t be bothered with it anymore. Akira feels the same way, especially with Kou gone, but didn’t ditch because she thought she had to go.
She thinks she’d have more fun if Kou were around, so she asks him to come back to school. When Kou doesn’t immediately refuse and seems to hesitate, Nazuna seemingly gets miffed and suddenly splits. Kou follows after her, asking if she’s angry and why, but Nazuna doesn’t feel like spilling it out, and is clearly still mad, so she flips him off and does her vampire warpspeed thing. Kou looks for her all night, without success.
Finally, in that magical in-between time just before sunrise, Kou falls on his face while climbing some stairs, then uses his receiver watch to call Nazuna. She responds, and he proceeds to tell her that while he doesn’t really “get” fights like the one they’re apparently in, but he wants to make up with her. With that, Nazuna suddenly appears, and is once again as honest with him as he was with her, saying she was “ticked off” by him hesitating after Akira asked him to come back to school.
Turns out she misunderstood; Kou hesitated because he wasn’t sure how to tell a human friend that couldn’t go back to school because he wanted to become a vampire. With that cleared up and the two well and truly made up, Nazuna notices the blood from Kou’s tumble, and proceeds to kiss him in order to drink it, remarking that “a lot came out”. She liked how he said human friend, and that it suggested he had a vampire friend too. Kou may not know this since she’s his first, but vampire friends do kiss.