|Japanese voice actor||Ayako Kawasumi,|
|English voice actor||Kat Cressida (Tokyopop dub), Brina Palencia (Funimation dub)|
Natsuki Mogi (茂木 なつき Mogi Natsuki, "Natalie") is Takumi's initial love interest, and one of the few characters who does not get scared when riding in a car being driven by Takumi. She is known to have been with at least three males in the series: Miki (Takumi's classmate), "Papa", and Takumi. Before she hooked up with Takumi, she engaged in enjo kosai to make some extra money with a middle-aged man driving a white Mercedes (nicknamed "Papa"). It is also revealed in First Stage that Miki, Takumi's classmate, has had sexual relations with her before. After getting to know Takumi, she falls in love with him and ends her relationship with "Papa". Mogi decides to free herself from her stained past by working hard to enter a university in Tokyo.
The status of her relationship with Takumi is somewhat unclear at this point: in volume 17 of the manga (and at the end of 3rd Stage), she and Takumi appear to mutually break up as they are going their separate ways; however, she appears in the first episode of 4th Stage in a flashback sequence where she and Takumi promise to find each other again.