It's been a while since i played HDN 1 and i havent gotten HDN 2 yet so I'll do my best.
Neptune/Purple Heart: Named after the Sega system "codename: Neptune" that never was made though was supposed to be competing with XBox, Wii, PS, etc.
Noir/Black Heart: Named after the playstation and Sony in general.
Blanc/White Heart : Named after the Wii and Nintendo in general.
Vert/Green Heart: Named after The XBox, and Microsoft in general.
Note: all there realms reflect the systems and companies. Lastation is very "steampunky", Lawee is very almost kiddie amusment park looking with a lot of over the top cutness, and Leanbox is very high fantasy, also Pleneptune is said to be the most technologically advanced.
Arfoire: named after the R4 memory card usually used for pirating games.
Compa: named after Compile Heart the company that made HDN 1, generally Moe games thus why she is made to be such a Moe character
IF: Named after IF, the company that designs primarily phone based games thus why she has so many phones
Nisa: Named after NIS (the company) and reflects this in her flatness and offense she takes in being called flat, as well as her drive to be the "hero of gameindustri".
Gust: Named after the game company Gust and is reflected in her alchemy and overall appearance that reflects the Atelier games.
5pb: A company that does game manufacturing and music label for both games and anime, thus why she is the music diva looking character
Red Heart: Red Entertainment
Histoire: This could be any number of things not exactly sure which though.
-All CPU's are rather indifferent to one another and all especially so towards Neptune although after a while in HDN 1 they will maybe join you.
-IF, and Compa are both friends of Neptune and aid her along her journey to save Gameindustri. They are also eventually aided by NISA and Gust though they only play support roles and bit parts rather then a large overarching portion of the game.
-Arfoire and Historie are both parts of the same Goddess though dont see eye to eye on things involving how they want to act on the world of Gameindustri