Momoka is Vivy's first human fan and friend when she was still finding her way to make people smile with her singing. She is also the one who gave Diva her name as Vivy, as she has the same image as the Princess Vivy on Momoka's hologram picture book. They first met when Vivy helped her when she got lost in NiaLand, thus making Momoka fond of her, which eventually gave her a teddy bear robot as her birthday present.
Her death made Vivy distraught, to the point that she disobeyed Matsumoto just to save her even though Matsumoto pointed that it was an accident, but made her determined to proceed with the singularity project to avoid such accidents in the future.
Matsumoto's partnership with Vivy is a bit strained at first, as she thought he was a virus that infiltrated her Archive server. He was very boastful at first as he was a Super AI from the future and saying her Archive server is very "antique".
Most of the time, she disobeys Matsumoto's instructions, as for her it was not very logical and reasonable not to save humans, and do what her mission is - to make people smile with her singing. As time passed by, Vivy became reliant to Matsumoto's instructions as it was their mission to save the future from being destroyed.
Matsumoto is also became very fond of Vivy as time passed by, as it was evident that he still cares for Vivy, that even though she lost her memories and rebooted back to being Diva, she still saved her from falling from the zodiac stage rooftop, pushed her away so that she won't suffer any more damage as like what happened to her before rebooting, and even trying to save her from the virus that will delete her Diva personality.
After Vivy got reconstructed in an unspecified time at the end of the series, Matsumoto mellowed out while greeting her and telling her original mission - to make people smile with her singing.