Leona is the reason why Jack enrolled at NRC: when 13-year-old Jack saw Leona playing spelldrive on TV he decided he wanted to play in a game alongside him and, after receiving his acceptance letter, he started training nonstop for the tournament of Book 2.
When Leona is not what he expected Jack asks, “What happened to the man you used to be?,” but as they presumably never met before NRC and Jack would not have known the man that Leona presumably used to be, it is possible that Jack’s frustration came from Leona being different from the assumptions Jack built up in his head after seeing him on TV (Leona: “Your dreams got nothing to do with me!”).
In Book 7 Ace observes, “With great power comes a whole bunch of people pinning totally unasked-for hopes and fears on you.” He was discussing Malleus at the time, and it is possible a point that the two princes have in common.
When Jack stands up to Leona early in Book 2, calling out the “disgusting spectacle” that is the practice spelldrive match against Cater, Ace, Deuce and Grim, Leona responds, “Pretty bold, frosh. I guess I can respect that,” and relents.
When Jack betrays Leona, Ruggie and the entire dorm in Book 2 Leona calls him a “filthy traitor,” which may have effected Jack more than he lets on until Book 7: Jack’s dream seems to be of a recreation of the interdorm spelldrive tournament where a dream version of Leona emphasizes the importance of skill, teamwork, and “hearts burning with drive!,” while Jack joins the chant of, “Long live the king!”
(Azul: “I’ve suddenly developed a much fuller appreciation for how terrifying Malleus’s signature spell is.”)
The dream-infiltration group reflects on the situation Jack faced in Book 2, with Silver explaining, “Turning against the housewarden of your own dorm…not to mention someone you admire…considering Jack had only just started school at Night Raven, that must have taken a lot of determination for him,” and Ortho commenting on the “heavy mental toll” the situation must have taken on Jack.
The group struggles with how to awaken Jack as Jack’s admiration of Leona being reflected in the dream meant that Leona was made even stronger than he is in reality.
Dream-Leona still calls Jack out for having poor technical skills, but he also goes to Sebek’s aid after he ends up outside the playing field, saying, “You don’t have any of the skill or moves it takes to be a back fielder. But you still never slowed down. That takes some serious guts,” and helping him to his feet. (Jack: “Leona’s respectful even of his competitors. That’s incredible.”)
Idia observes, “this dream’s probably changed (Leona) into someone worthy of Jack’s genuine respect…he hasn’t turned into a saint or anything, but he does value sportsmanship and never goes for dirty plays.”
After Jack awakens he reveals the extent of emotional damage, saying, “I wanted so desperately to make you guys realize that. But I couldn’t do anything by myself. That’s why I… I… *sniff*,” possibly in reference to betraying Leona and their dorm.
Jack is not pleased by students of darkness referring to Leona as their king in Leona’s dream (“Leona ain’t your king. He’s our housewarden!”), and it is Jack who awakens Leona by telling him to remember who he is in possible character development for Jack, who had such an issue with Leona being who he is back in Book 2 (“What happened to the man you used to be?”).
After Leona escapes the abyss Jack begins to cry, saying that, while Leona and Ruggie are both still jerks, he prefers the real them over fakes,” and he is “so glad (they) woke up.”
Twisted Wonderland Reference Note 