When Deuce sees financiers in Fleur City he says, “Trey’s made me those things before!”
Deuce struggles to “think of something that Riddle and Trey don’t already have” while shopping for souvenirs in Clock Town, ultimately deciding to get them frosted cookies (“Trey’s taught me a lot about cooking”).
Sebek reacts with displeasure when Cater refers to him with the “-chan” honorific, much like Deuce himself did in Book 1.
In Book 1 Trey reassures Deuce that that is just how Cater shows he cares, and in Book 7 Deuce quotes Trey word-for-word. (Deuce’s wording was changed for EN: the meaning is the same but it is no longer Deuce directly quoting Trey’s response.)
Trey holds Deuce back from fighting another student at the beginning of the Wish Upon a Star vignette, and again at the end when Deuce becomes frustrated with Idia.
When Deuce threatens bullies during the event, successfully driving them away and saving the wishing stars, Trey says he had been intending to step in but Deuce had not risen to their bait: “That took real self-control. You did good, Deuce.”
Trey agrees with bullies that dancing in their stargazer outfits is embarrassing (“Which is why I was trying to avoid being seen”), but Deuce does not understand, saying that Trey looks great.
During White Rabbit Fes Deuce is similarly embarrassed by his outfit until his mother and the rest of the group reassure him, and by the end of Wish Upon a Star Trey says that Deuce was right: “this isn’t the time to worry about being embarrassed. Thanks for the reminder.”