Julian is Joni's older brother, with an age difference of 9 years. The siblings' relationship first kick started as a form of sibling rivalry, with both constantly getting into small fights and/or arguments, including jests about the other's weaknesses or things they lack, sometimes even accidentally. Their constant bickering tends to result in (comical) violence, as Julian tends to smack Joni on her head or pull the top portion of her hair.
Joni's reckless and carefree nature often clash with Julian's serious demeanor, leading to disagreements. Julian kept Joni in check of her attitude and actions, and would reprimand or physically confront her whenever Joni did something wrong. As stated by Julian, Joni was known for teasing him for not having a girlfriend and/or a friend, and would often seek for opportunities to blackmail him.
Overall, despite the two's rivalry and constant bickering, Joni greatly looks up to her brother, and is grateful of his guidance during her revision over her academics. At some point in Starstruck!: Fandom, due to misconceptions, Joni mistook Julian for the portrayal of her idol, Monster Ranger, thus displayed admiration to Julian- a side of Joni that greatly weird Julian out.
Joni was known for being close friends with Mia ever since kindergarten. Their personalities are somewhat contrasting; with Joni being more sociable, reckless and cheerful and Mia being socially inept, self-cautious and pessimistic. Throughout their childhood, Joni was known for protecting and defending Mia in times of crisis from bullies in school such as Sofia. Mia, on the other hand, often cares for Joni's well-being and often advocate with her opinions and choices.
Joni was known for praising Mia for her talent and friendly nature in front of their classmates.
Emilia is one of Candy Series' protagonists alongside Joni and Mia and is also Joni's best friend. Joni and Emilia's relationship started in Reaching for the Stars: Friendship. Emilia was shown to be strict towards Joni to the point where she seemed like she hated her at first, but she lost all of the hatred when Joni stood up for her and called Emilia her friend. Since then, she and Joni, alongside Mia, became best friends.
Corey is a supporting character of Candy Series and also one of Joni's friends. He made his debut in Healthy Pretty Girls: Diet. Corey and Joni started their relationship in Healthy Pretty Girls.
SofiaUpon first appearance, both parties displayed hostility and bear cold shoulders towards to opposite, often calling each other names and badmouthing each other. Their animosity lasted for a long time throughout and only on a few occasions were they nice to each other. One example was when Sofia tried to help Joni to conquer her airsickness during their flight in a plane to Langkawi. Another example was when Joni, along with Mia and Emilia, paid a visit to Sofia's house to see how was her recovery from her faint. Despite the times when they actually treated each other with sincerity, the two still remained reluctant in accepting each other.
However, their relationship soon improved in Spick & Span: Cleanliness. When Joni frustrated and exaggerated over her being partners with Sofia during the school's cleaning day, Richard corrected her, stating that Sofia is not a totally bad person. Joni then recalled over what Richard has described of Sofia, and then finally came to the conclusion of accepting Sofia (even admitted that she sees Sofia as a sincere and caring person).
Joni and Charles' relationship was limited to them being enemies and interactions limited into bickering. The two had been rivals ever since they met in Everybody's Favourite Friend: Amity due to the fact that Joni was against the idea of Charles and Mia being friends.