RelationshipsNinjaNomicon tells Randy that the Ninja friendship is a weight that the Ninja cannot carry, Randy ignores it and stays dedicated to their friendship. However, his ninja duties and friend duties prove to be challenging for Randy, and many times this has resulted in major conflicts between them, like in "30 Seconds to Math", when he keeps on Ninja No-Showing (NNS), abandoning Howard to fight the Robo-Apes. The two friends do have some fights, but no matter what the condition is, they often forgive each other.
Randy can be quite uncaring and rude to Howard, like in "Monster Drill" when he laughs at Howard, in "Nukid on the Block" when he accuses Howard of not having any idea about having a duty, and in "Evil Spirit Week", when he get angry at Howard and didn't take him seriously when Howard kept saying something was wrong with him. When Howard gets the upper hand, like joing the Mustache Society without Randy or getting the credit for winning a game by helping Randy at the last second, Randy gets jealous and holds a grudge against Howard. He also tends to underestimate Howard and his abilities, which can sometimes result in more trouble for both or one of them, like in "Escape from Detention Island". Once Randy comes to terms with his mistakes, however, he works hard to make it up to Howard and mend any problems between them. Howard also causes his fair share of their problems, which Randy rarely doesn't forgive. It is shown that Randy cares for his best friend deeply, risking his life on occasions (like in "Ninja Camp") and throwing the Ninja Mask into a bonfire in order to save Howard from the Tengu ("Evil Spirit Week"). Throughout all of the craziness in high school, Randy appreciates Howard's loyalty and companionship. In "The Ninja Supremacy", Randy acknowledges that Howard is a jerk, but tells him he won't forgot that Howard's always been there for him.McFists of Fury", he finds out that his role model is actually responsible for the robots that try to get rid of the Ninja. He does not expose McFists' dark secret to the public, possibly fearing that no one would believe him. However, he does in "McOne Armed and Dangerous" when he gets frustrated at McFist, but covers up the truth when it causes McFist to get stanked. He says that as the Ninja, he is boycotting McFist's products, but as Randy Cunningham, he will still be first in line to get them. Randy seems to be nervous when meeting McFist out of his Ninja attire and often strings large suspicious sentences together if he has to talk to him, despite the fact that he still thinks that McFist's stuff is cool. As the Ninja, Randy despises McFist for all the trouble he causes him. Sometimes, though, Randy will ignore their statuses and help him, although he's often hesitant to do so, like in "Rise of the Planet of the Robo-Apes" and "Flume-Igation".
Viceroy is the one responsible for making the robots that attack the Ninja. Despite their times together, Randy has only interacted with Viceroy as "Randy Cunningham" once, in "Weinerman Tested, Cunningham Approved", and the rest of the time Viceroy knows him as the Norrisville Ninja. Randy doesn't appreciate having to deal with Viceroy's creations, but he usually can beat them. Although they're usually antagonistic toward each other, Randy helps Viceroy on occasion and the other way around. In "Monster Dump", he saves Viceroy's pet Nicholas in exchange for Viceroy to take a vacation from helping McFist try to destroy him. In "Dawn of the Driscoll", Randy uses Viceroy to help him defeat Jerry Driscoll before he can destroy the world.NinjaNomicon explains it to him in "So U Think U Can Stank". The only relationship Randy really has with the Sorcerer is being his arch-enemy. He has encountered his Stank many times, and has destanked many monsters created by it. They finally meet face-to-face (but not in person) in "Raiders of the Lost Nomicon". The Sorcerer strongly resents the Ninja for keeping him trapped in his prison, but doesn't know his secret identity. When he finds out he has to fight the Sorcerer in the final battle, Randy is both terrified and excited. Randy finally met and fought the Sorcerer face to face in "Randy Cunningham: 13th Century Ninja", assisting the First Ninja in sealing him.
Randy, who usually doesn't care much about romance, seems to have a crush on Theresa whenever she's around, treating her with kindness and respect. Although his crush on Theresa isn't as huge as her crush on him, Randy seems to be aware of her feelings, and does genuinely care about her. In "So U Think U Can Stank", Randy destanks Theresa, assuring her that everything is going to be alright afterwards. He wants her to see him in good light, and either blushes or reacts with surprise when she grabs his hand. Having to tell her that he's not a hero in "Sorcerer in Love 2: The Sorceress's Revenge" frustrates him, even though he knows it's the only way for her to let go of his hand. To destank her, Randy, as the Ninja, apologizes for ignoring her and flirting with Heidi (while his body was under NomiRandy's control) and gives her a bouquet of roses in "Shloomp! There It Is!".
Though Randy occasionally finds Bucky's zings annoying and he calls him a "Brown-Noser" in "Attack of the Killer Potatoes", he is actually really nice towards him, considering the Ninja constantly has to save and destank him. However, his intentional kindness has led to problems, like when he despsies Bucky's song but doesn't want to hurt his feelings in "Everybody Ninj-along". Occasionally, Randy isn't as friendly to Bucky. In order to go to Mt. Chuck, Randy tricks Bucky with word play in "Monster Dump", but he makes it up by preventing Bucky from getting a month of detention. Another case of this is in "True Bromance" when Bucky's brief comradery with Howard in makes Randy jealous, who tricks Bucky and his friends Dave and Pradeep to get locked outside on the roof. But when they are stanked and Howard is the thing they hold most dear, Randy, without the mask, apologizes to them.Der Monster Klub". He's even more enraged when Bash lies about being the Ninja and gets attention from the entire school, but still saves him from danger in "Bash Johnson: 11th Grade Ninja". Randy isn't as afraid of him as many other students are, but still doesn't like messing with him. However, in "Pranks for Nothing", he plans revenge on Bash for his pranks, which goes completely out of control. Also, in "Raiders of the Lost Nomicon" he is willing to attack Bash to recover the NinjaNomicon. So U Think U Can Stank". He has stated that he has known her his entire life. He probably noticed that it is best if she doesn't notice him, since if she found out that he is the Ninja she would most likely reveal that on her show, like in "Gossip Boy" when Howard almost tells her that Randy is the Ninja. He still is willing to help her, like in the episode "30 Seconds to Math", when he goes to retrieve her guitar from the Robo-Apes instead of staying to play with Howard. Heidi attempts to keep Randy and Howard inside the house during "Grave Puncher: The Movie!" and later gets the blame when trying to explain the situation. Feeling guilt, Randy takes the blame on Howard and himself, earning respect for himself from Heidi, but she still manages to deliberately mispronounce his name, much to his annoyance. In "Shloomp! There It Is!" she is unsettled by NomiRandy hitting on her and declares to a stanked Theresa Fowler she barely knows Randy, but after seeing how Randy (through the Ninja) solves the situation by apolozing, Heidi says maybe he's not so bad after all, though still getting his name wrong. In "Welcome Back Catfish", Randy admits he finds Heidi attractive in certain lights, much to Howard's disgust.
Flute Girl does not think that Randy and Howard are very smart, and Randy finds Flute Girl's know-it-all personality annoying sometimes. Flute Girl seems to regard Randy and Howard as idiots, as shown in "Monster Dump", "Nukid on the Block" and "The McHugger Games". However, she thanks Randy a lot as the Ninja (not knowing his real identity).
Considering Julian to be one of his best "classmates", Randy mostly appears to have mixed feelings about him while never showing ill-will towards him. In the episode "The Tale of the Golden Doctor's Note", Randy has sympathy for Julian and teams up with him to get the doctor's notes. Because Julian became terrified and got stanked, Randy gives him the only doctor's note they were able to claim instead of letting Howard have it. They also seem to bond in "Der Monster Klub". Randy does find Julian bothersome in "Julian's Birthday Surprise", though, as Julian steals his bag with the chaos pearl and uses its power to create havoc. Even when apologizing for Howard, Randy is not thrilled about hearing Julian's history about desiring to be a magician, and he is immediately relieved when the Nomicon starts glowing for him to shloomp in. When Julian is fully mad with power, Randy admits that his behavior isn't normal and he isn't a shoobiopath. In "Winner Takes Ball ", he and Howard searched for Julian in the Land of Shadows.
In "Viva El Nomicon", Randy thinks Debbie was being ridiculous about his and Howard's spanish being awful, although she proves to be right. Randy, as the Ninja, asks for her help when he needed to defeat a Mexican Death Bear, which was attacking the school. In "Night of the Living McFizzles", Debbie challenges Randy's courage. Because he was nervous of what she and Theresa would think of him, Randy lies and acts as if he hadn't been afraid. His realization about how Debbie Kang's snooping has ruined a lot of things he enjoys leads him to use his Ninja persona to ask for her to not ruin the soupsicles in "All the Juice That's Fish to Swim". When he figures out he's wrong about them, he asks her to expose them. Throughout this and saving her from Howard's mutated form, Randy is pretty nice to her. In the end, he apologizes for telling her what to write, and he doesn't seem to know yet that Debbie has decided to discover his, the Ninja's, secret identity.Dickie to him in "Stank'd to the Future", seeing him doing and allowing unfair tricks during his stay in the camp, and his cruel and psychotic attitude towards justice in "Ninja Camp". When Mac Antfee returns in "Enter the Nomicon", Randy is horrified and skeptical about believing that Mac Antfee has changed and become a good guy, mainly because of the Ninja Camp experience. He accidently reveals his secret identity as the Ninja to Mac and reverts Mac to his old self, but Randy eventually gets Mac Antfee mind-wiped in the Nomicon, making him a permament good guy. It is unknown whether or not they're finally on good terms.