Neptune is the fourth wall breaking main protagonist of the Neptunia series (a fact that she is quick to mention) and the personification of Sega Consoles.
As the Neptunia series has many dimensions (Hyperdimension, Ultradimension, etc...) that the games take place in, there are many Neptunes in the series with varying, but similar personalities. Usually, she's depicted as the CPU (Goddess) of Planeptune and the older sister of Nepgear and a friend and rival of Noire.
However, this can change, such as the sister-less human Neptune from the Ultradimension or the Neptune from Superdimesion Neptune vs Sega Hard Girls who was turned into a Motorcycle and 'lovingly' given the nickname 'Crap Bike' by Segami.
- Neptune, aware of Noire's tsundere crush on her, loves to playfully tease her about it.
- Neptune teasingly suggests that Noire loves her on multiple occasions.
- A lot of official art pairs Neptune with Noire.
- She shares a pudding with Noire in Re;birth1.
- In mk2, Neptune goes to Noire to ask her about what swimsuit Noire thinks she would sexy in.
- Neptune, Ultradimension Noire, and Plutia take a bath together in Victory
- She takes a bath with Nepgear and Uzume, in Megadimension Neptunia.