In Hyperdimension Neptunia, IF is very close to 5pb. She was first a fan of 5pb., eventually learning her name, Lyrica then trying to help her overcome her shyness. She tries to help 5pb. sell her music and got angry when a customer was complaining about how bad it was.
In Hyperdimension Neptunia Victory, it was revealed that 5pb. and MAGES. are related, but it wasn't revealed how they were related until Hyperdimension Neptunia Re;Birth3: V Generation, where they are revealed to be sisters, with 5pb. being the older sister, and MAGES. being the younger. This is similar to the relationship of the companies they are based on, with 5pb. being older than MAGES.