Adorkable: Just like both of his parents, Kairi does prove that he could just be awkward as any other characters, but is mostly this when he's around Hayato of all people.
Amazingly Embarrassing Parents: How he thinks of Sora. Although, the real reason is far more complicated.
Apocalypse Maiden: Due to having Yoru posessing him since he was just a child, Kairi becomes the next vessel of Nephilim due to Yoru's constraint Knightmare powers if Kairi were unable to gain control of it. As proven in Heaven's Wish...
Badass: He's capable enough to out-Badass Hikari in terms of power and even then on able to hold himself in battle even without relying on Yoru.
Badass Adorable: When he's being Adorkable, you can't help but say Aww~~ on him.
Badass Bookworm
Badass In Distress
Beneath the Mask: Portion of Heaven's Wish are taken from his perspective and provides an alternate look at his personality. Even more happens in -Another Side- due to acting the protagonist.
Berserk Button: You do NOT want to hurt either his parents or his friends (especially Hayato), or he'll snap out HARD. Another bigger button happens when Kairi meets Kazuto's attempted killer (or, Hayato's killer), and the results were not pretty in the least...
Break the Cutie: In Heaven's Wish due to Sancraid's Mind Rape. Another worst one would be Hayato's Heroic Sacrifice for Kazuto, Kairi really can't get a hold of it...
Broken Bird
Can't Live With Them, Can't Live Without Them: With Yoru. Justified though, considering Yoru's the reason he would be able to live because of his sickness.
Celibate Hero: Even despite the Ship Teasing between him and Rita for the first two seasons, Kairi is actually this, considering how he really does NOT appreciate romance. Well... probably except Hayato anyways...
Character Development: -Another Side- has Kairi becomes mellowed down a little after Hayato's revival. Although he still is a jerk, he does shows a nice side over times, as seen with Hikari.
Childhood Friends: With Rita.
Combat Tropes
Combat Pragmatist: Courtesy of Knightmare.
Cool Keyblade: His Celestial Tears Keyblade, and Stormfall.
Elemental Powers
Casting A Shadow
Fire, Ice, Lightning
Flash Step
Full-Contact Magic: Similar like his mother.
Magic Knight: Compared to either Sora and Rini, Kairi is a much more balanced version but probably prefers speed and darkness magic.
Red Mage
Second Hour Superpower: Though it takes him three seasons to do so, but by the time -Another Side- rolls on, he finally manages to tap into a full Synchronization with Yoru not long once he learns that it took both of them to "be as one". He keeps getting more and more powerful from there.
Spellblade
Throwing Your Swords Always Work
The Corruptible
Cry Cute: Happens a lot during -Another Side- but probably that takes the cake when Hayato died.
Dark Is Not Evil
Deadpan Snarker: Aneven harsher snarker than his mother would be.
Defrosting Ice King: Eventually melts thanks to Hayato and later Hikari's efforts.
Demonic Possession: Gets into a forced one by Sancraid in Heaven's Wish with Yoru. In Accel through INFINITE, this is how he's able to use Knightmare by letting Yoru taking over his body, at least until he realizes that they need to be fully synchronized to achieved its full power.
Deuteragonist: In ~After Story~ REGIOS.
Driven To Suicide: Nearly driven into this following his massive Despair Event Horizon until both Hikari and Yoru snaps him out of it.
Enemy Within: Subverted. Most of the characters thinks Yoru is this to Kairi, however it later revealed that Yoru is Good All Along after the events in Chronicles of Miracles.
Vitriolic Best Buds: In fact, his relationship with Kairi is pretty much this.
Even The Guys Want Him: Yang is implied to have a crush on Kairi, Hayato outright confessed he likes him, and let's not get into the whole Ship Teases between him and Hikari.
Expy
Four-Temperament Ensemble: The Choleric.
Get A Hold of Yourself, Man!: Does this to Hikari in ~After Story~ arc and to an almost-possesed Rita in Night Vision arc. Hikari later returns the favor to him by snapping him out of his suicidal depression.
Green-Eyed Monster
H-P[]
Hair Decorations
Heterosexual Life Partners: Possibly is this with Hayato, at least until he confessed he loves Kairi.
Heroic BSOD
Ho Yay: Has a lot of these with either Hayato and Hikari, especially the former.
Icy Blue Eyes
If It's You, It's Okay: Implied to be this to Hayato, and later Hikari.
Ill Boy: What he used to be during his childhood, it's not until Yoru's possessing that he manages to cure off the disease. At least until it bites him back hard...
Jerk With A Heart of Gold: Even though Kairi might be the massive Jerkass right after Gale, but he does shows that he has a good side, especially when he's around Hayato.
Mind Rape: Happens to him in Heaven's Wish arc courtesy of Sancraid.
Morality Pet: Hayato is this for him and he's also this for Yoru/Nephilim.
My God, What Have I Done?: In Heaven's Wish when he realized he nearly killed Sora, after he admits that he really does loved him.
Only Sane Man: Like his mother, he is this around his childhood friends and also to the main casts.
Not So Above It All: Although, he can be just as weird as his friends would be. Even Yoru calls him out of it.
Platonic Life Partners: With both Rita and Asuka. And this is despite the heavy ship-teasing between him and the former.
Q-V[]
Red Oni, Blue Oni: The Blue Oni to Hikari's Red Oni. And also to Yoru.
Red Eyes, Take Warning: Whenever Yoru possesed him, and it is not a good idea to pissed him off at this state.
Mismatched Eyes: When he manages to achieved Soul Synch, both of his blue eyes turned gold and red respectively.
Shipper On Deck
Sir Swears-a-Lot
Slasher Smile: Whenever Yoru possesed him. And when it's not, it is NOT a good sign either...
Soul Jar: A possible one for Nephilim if he ever loses control of Yoru's Knightmare powers.
Superpowered Evil Side: Yoru can be this for Kairi, at least before they hit Soul Synch ability.
Talking With Himself: Has a habit of doing this from the Night Vision arc and onwards. Granted, Yoru constantly annoys the hell out of Kairi, even after they resolved their problem.
Tsundere: Tsun tsun towards everyone, Dere dere towards Hayato and probably Hikari.
Turns Out Like His Mother: He has a lot more in common with his mother than his father, much to Rini's dismay (who only wishes that her son won't be turn like her).
W-Z[]
"Well Done Son" Guy: Inverted. Sora tries his hard to make Kairi proud of him, even despite all of his efforts makes Kairi a lot more embarrassed and annoyed.
What The Hell, Hero?!
Would Hit A Girl: Has no qualms of hitting Asuka whenever she's being stupid. He tends to get called out on this, but he ignores it anyways.
The Woobie: Well... It isSchool-Side Chronicles anyways.... And Kairi's backstory is hell lot of Tear Jerkers abound...