Choji and Karui’s coupling is revealed in Boruto, the sequel series to Naruto starring Naruto’s son, from whom the series gets its name. Alongside Boruto, much of the rest of the series’ teenaged cast is comprised of children of established characters as well. Metal Lee, for example, is the son of Rock Lee. He not only resembles his father in appearance but fights with the same Strong Fist style of taijutsu.
In Naruto, Choji, Ino, and Shikamaru comprise Konohagakure’s Team 10. In Boruto, Team 10 is made up of their children. Inojin is the son of Ino and one-time Team 7 member Sai; Shikadai is the son of Shikamaru and Sunagakure’s Temari; and Chocho is the daughter of Choji and Karui. Their teaming up marks the seventeenth such combination of members of each of their respective clans, known as Ino-Shika-Cho.
Some fans in the Reddit thread theorize that Choji and Karui’s pairing was primarily intended to preserve Ino-Shika-Cho into a new generation. While Choji seldom interacted with Karui prior to their marriage in meaningful ways, he also had few meaningful interactions with women in the series not otherwise intended for a romance with another character. Thus, series creator Masashi Kishimoto may have simply paired Choji with one of the few remaining eligible women in order to ensure that he ended up with a child capable of joining the next generation of Ino-Shika-Cho.