Demon Bull King
The Demon Bull King is Red Son's father.
In "Monkie Kid: A Hero is Born", it is shown that Red Son is extremelly loyal to his father and will do whatever it takes to make D.B.K. proud of him. Red Son was the one who freed his father and wanted to get rid of MK for him.
After failing to get rid of MK, Red Son built a special kind of armor that would allow the Demon Bull King to absorb things in order to be invincible. Despite everything Red Son does for him, D.B.K. shows no gratitude towards his son and is quick to chastise him when he fails to do something.
In "The Great Wall Race", he ignored Red Son as he suggested entering the Great Wall Race until he and his wife realized that it could be a good way to crush their son's ambitions, and so both him and Princess Iron Fan entered the race. When Red Son passed by them he accelerated and ended up crashing against a mountain and found himself unable to advance, possibly due to all the time he spent trapped under a mountain and her son made it farther than them, even though he didn't win.
In "Revenge of the Spider Queen" it was shown that Demon Bull King cares about his son in his own way. When he found out Red Son escaped the Spider Queen, he was visibly proud of him and declared that he couldn't wait to see the Spider Queen get defeated by his son. When Monkey King said that the Spider Queen will eat Red Son and Princess Iron Fan, it caused him to become enraged. Once free from the Spider Queen, DBK left to save his son and freed him from the cocoon that Spider Queen trapped Red Son in. After the Spider Queen had been defeated, DBK agreed with his son to not tell Princess Iron Fan about the incident and called him "son" out loud, which made Red Son very happy.
Princess Iron Fan
Princess Iron Fan is Red Son's mother. The two had little interaction one on one. Most of the time she seems to be annoyed by his antics and possibly has a low opinion of him since she taunted him when the Bull Clones lost the staff again. However, Princess Iron Fan seems to care about him since she talked her husband out of chastising their son for failing to retrieve the staff.
Despite everything, Princess Iron Fan does indeed care for her son since she protected him from the rage of her husband when he was possessed by Lady Bone Demon while Red Son also showed concern for her when she approached her now freed husband and was happy to see them together and his father back to normal.
MK is one of Red Son's adversaries.
When Red Son first met MK, he gained an instant disliking to him due to MK crash landing on top of Red Son after a bird makes him fall, ruining the Demon Bull Family's moment. After the Demon Bull King attempted to kill MK, Red Son stopped him, but only because he wanted to do it for him.
Red Son met Mei when she rescued MK from him, believing that they were just racing, Mei mistook Red Son for a friend of MK's and wanted to invite him to play video games with them until she found out he was DBK's son. After MK is presumed to be dead, they almost fought with each other had MK not arrived in his Cloud Jet.
In "Revenge of the Spider Queen", Mei is at first distrustful of Red Son after he shows up on the Team Dronecopter and tackles him along with Pigsy and a reluctant Sandy, but slowly calms down after Red Son reveals that the reason he came to them was because his father was trapped by the Spider Queen and that he had some of the Spider Queen's venom that could be useful to make an antidote. After MK makes the decision to let him help them defeat the Spider Queen, she reluctantly agrees.
When Red Son brings them to the Celestial Realm to get the ingredientes they needed for the antidote, Mei teased Red Son upon realizing he doesn't know where said objects are and refuses to let Red Son go after the Immortal Peach on his own but he tells her to stay behind "like a good dog", even patting her on the head, resulting on Mei biting him. Once they are in the Celestial Realm, the team is divided in three groups, with Mei paired up with Red Son. While looking for an Immortal Peach, Red Son is constantly annoyed by Mei's quirky behavior. Mei then reminded Red Son of the time he helped MK defeat his father (because he was possessed by the Lady Bone Demon), making him angry and defensive. Mei then claims that since he was helping them he was now a hero and went on a tirade about how heroic he was, making him even angrier and he destroys her phone after she takes a live stream with him but she quickly pulls another one from her sleeve. Red Son then makes a note to put her next on his hit list while casually placing her second phone in his coat's pocket. However, he later climbs on Mei's shoulders to get the peach while Mei tried to talk about the Great Wall Race but Red Son only mentioned how Mei (and MK) crashed his car, with Mei only saying "we wreaked a lot of stuff".
After the team gets all the ingredients and Red Son gets ready to create the antidote while talking about how he was going to reshape the world to his liking once the ordeal was over, Mei says that Red Son is "amazing" and both her and MK think that Red Son's speech was a great "hero speech", which once again causes him to yell at them that it was a villain speech. While the team fought against the Spider Queen, Red Son attempted to protect Mei but it only ended up in both of them captured.
When DBK frees his son from the cocoon Spider Queen wrapped him in, Red Son in turn frees Mei and when he is injured during the battle Mei helps him walk by placing his arm around her shoulder. When Mei tells his father about how Red Son acted "like a real hero", he once again yells at her that she is lying and that he is evil before Red Son teleports himself and his father away.
When Pigsy thought MK was killed by the Demon Bull Family, he attempted to fight Red Son himself until Mei stopped him so that she could fight him herself.
Pigsy is at first very distrusful of Red Son and immediately tackled him along with Mei, even dragging a reluctant Sandy along but slowly calms down after Red Son reveals that the reason he came to them was because his father was trapped by the Spider Queen and that he had some of the Spider Queen's venom that could be useful to make an antidote. Pigsy and Mei engaged in get another fight with Red Son before MK makes the decision to let him help them defeat the Spider Queen and Pigsy reluctantly agrees. The two barely interacted during the ordeal unless it became necessary.
When MK's team is seemingly being attacked by an unknown ship, Sandy stopped the ship with just one hand and it collapsed. As soon as Sandy saw that Red Son was the pilot he was visibly shocked and withdrew his hand. He was later forced by Pigsy to tackle Red Son. Sandy later tried to stop Red Son, Mei and Pigsy from fighting each other. The two barely interacted after that.