Neptune is the first CPU IF met while IF is the second maker character Neptune met. Despite large differences in personality, she is one of Neptune's closest friends. However, she is serious so if Neptune slacks off, she is going to get it. They have their occasional bickering with weight and body shape but nothing they cannot solve with some competitive gaming!
In the Ultradimension Neptune raised child IF.
In the original Hyperdimension Neptunia, IF worships Vert as her CPU. IF and Vert get along very nicely as a result. Vert tries very hard not to disappoint IF so she hides her boys love games.
Ultradimension IF was put in the care of Plutia and Neptune at the age of two and grew up with them. She came to like Plutia, actually referring to her as 'Plutie' similar to how Neptune did.
However, when she was five she suffered trauma when she saw Iris Heart beating up Arfoire. As a result, IF is terrified of Iris Heart and always speaks very carefully around Plutia to avoid angering her.
IF is one of Nepgear's closest maker friends. She was able to kick start Nepgear's transformation into her HDD in HDNmk2. IF cares for Nepgear, shown in the anime by preventing her from recklessly charging into Arfoire's trap.
Compa is IF's childhood friend. They are best friends with very different personality and are the first two to meet Neptune. IF plays the role of a protector to Compa. She is comically obsessed Compa with different incarnations of IF having pictures of her sleeping, refusing to share Compa with the other makers or wanting her to be an idol to take down Neptune.
In the original HDN, IF has a very friendly relationship with RED as a result of IF playing the role of "wifey" for RED.
Histoire and IF have a good relationship. IF works for the guild so she is entrusted with many tasks for Planeptune.