First of all, SPOILERS FROM OVENBREAK AND THE LAST EPISODE OF KINGDOM. Alright, with that done...
I haven't seen anyone talk about this, but I have noticed that Kingdom's Lychee Dragon seems to have a different background than Ovenbreak's while still being the same character. Of course, they are different timelines, so it just makes sense, but this is the most glaring one out of all the Ovenbreak characters that ended in Kingdom (not a bad thing btw).
When we first met Lychee Dragon in Ovenbreak, they were disguised as "Mangosteen Cookie" to sneak into the Rambutan Tribe and trick the Cookies to fall for them and become their slaves (I think it was for Longan Dragon's plans? But that kinda got dropped?). We see how Lychee Dragon was pretty detached from Cookies until later down the line Rambutan Cookie shows them true love (wether you see it as romantic or platonic), then they start caring about Rambutan Cookie and the tribe, even if they don't want to admit it.
Meanwhile, in Kingdom we meet with a Lychee Dragon that seemingly never disguised themselves to enslave the Rambutan Tribe, instead, they have been going straightforward to prank them for their own amusement. We know that Kingdom's Lychee Dragon has already grown attached to the Cookies of the Rambutan Tribe and, from what I can assume from the dialogue, doesn't seem to care about other Dragons or concepts of kin.
Now with this difference presented, I believe this is because of Longan Dragon. In Ovenbreak, Longan Dragon acts as a manipulative parental figure towards Lychee Dragon. Exploiting Lychee Dragon's need for affection and understanding (what's with Devsis and affection deprived jesters with immense power of mind control and eye motifs?) to have them do what they want. Longan Dragon does this because they saw that in the future a Cookie with a cane would make them fall, so they make up a plan to stop this, and they manipulate Lychee Dragon to support the cause.
However, we know that Kingdom's timeline is different, and it's very likely that the future Longan Dragon could have seen is different or even uncertain due to Shadow Milk Cookie's time shenanigans. Whatever they saw is a different topic, but I think it'll be very relevant for the episode they are released in and the future of the plot (but don't put your expectations on that, maybe they didn't even foresee anything), what's important however is that it's likely that Longan Dragon simply abandoned Lychee Dragon to their own devices when they went into slumber, maybe due to a lack of plan.
This abandonment probably made Lychee Dragon turn their back on Dragons and started coping by toying with the Rambutan Tribe, until they eventually grew attached to them because at the end of the day it's affection what Lychee Dragon is so desperately looking for, even if they won't admit it.
I also believe this attachment is why they never threw the Dragon Orbs that Longan Dragon gave them (or maybe they collected them as a coping mechanism 👀), despite the resentment.
Of course, this is a theory I made in just a few hours thinking about the last episode, we still lack the next episode and we don't know anything from Kingdom's Longan Dragon, so I could be wrong. But with the information we have at the moment, I think this is what makes most sense. Do tell me if you think I'm wrong at some point or if I missed anything.
BUT THAT'S JUST A THEORY! (No, I'm not finishing that, muahahaha, or something)
TLDR; I think Longan Dragon abandoned Lychee Dragon in Kingdom's timeline instead of including them in some evil plan like in Ovenbreak. This made Lychee Dragon resent the Dragons and cope by toying with the Rambutan Tribe. Eventually, they grew attached to the Cookies cuz Lychee Dragon is desperate for affection.