This article you can read the relationships of Fireboy.
FireMom is Fireboy's mother. Although they are not in common sometimes, Fireboy and FireMom talk to each other and share things.
FireDad is Fireboy's father. They talk to each other and share things, and Fireboy is even interested about him, such as in "FireDad's Job".
Fireboy and Watergirl are boyfriend and girlfriend, though they don't kiss or hug each other in many episodes. However, they do stupid things together in the school. They love each other since when they were in kindergarten, as seen in "Fireboy's Origins 2" and "Watergirl's Origins 2", and was mentioned in "Flashback Time".
Fireboy and ZungBoy are shown to be best friends. They hang out with each other in several episodes.
Fireboy and BlackGirl are shown to be best friends while hanging out with each other in several episodes.
Fireboy and Rockboy are close friends. However, when Rockboy is grumpy, Fireboy screams at him for the hard feeling.
Fireboy and Leafgirl are usually friends, but in "Endless Question Film", it was enough for Fireboy that Leafgirl is lame.
Fireboy and Icegirl show a friendly relationship. In "Fireboy & Watergirl Goes to School", Icegirl became a wild animal for Fireboy touching her.
Fireboy and Vanessa are shown to be friends. Their partnership was a possible.
Fireboy and Waterboy, as approval to a future brother-in-law, are close partners.
Fireboy and Water Dolly have a partnership as sibling-in-laws.
Fireboy and WaterMom are approval to a relative-in-law.
Fireboy and WaterDad had the approval in the premiere episode of the entire show, "Lavas & Waters"