His decks and playstyle has one common theme to it in terms of gameplay; he likes to overwhelm his opponents with high power and multiple stands, especially if it restands the Vanguard, and limit his opponent's options by retiring their units. It's also been said that Kai used to play Royal Paladins in the past.
Later in the series, he focuses on the Blazing Flare Dragon's superior ride and uses it during the first Regionals tournament, winning all his matches with it. This deck focuses more on retiring enemy units and units that gets advantage due to that.
After Aichi is corrupted by PSY Qualia, Kai switches his deck to the Amber Dragon build and focuses on beatdown strategies and applying pressure by retiring the opponent's rearguards when Amber Dragon, Eclipse hits.
Towards the end of the series, his deck is rebuilt to focus on Dragonic Overlord The End and cards that supports or gets supported by the Overlord series. However with this deck, he did not manage to defeat Ren to bring him back to his old self.
During season 2, he uses a Narukami deck, focusing on Dragonic Kaiser Vermillion as his ace to attack his opponent's front units thus lowering their attack force. This also helps to power-up his rear-guards like his wyvern units and he include Garuda to unflip his damage in order to reuse Dragonic Kaiser Vermillion effect.
Kai continues to use the Narukami clan utilizing the Eradicators with his deck. This deck utilizes Eradicator, Vowing Sword Dragon's effect to get rid of an important threat before going in for the win. In addition, he uses Eradicator, Dragonic Descendant ensure that even when his vanguard's attack doesn't go through the first time, he's set up for another, even more powerful strike.
It should be noted that while he does primarily use the Narukami clan at this point, he still keeps his unsealed Kagerō deck, though only Morikawa and later Miwa would use this deck.
After he gets Reversed by Takuto, Kai switches to a Link Joker deck that focuses on the Star-vaders series with Star-vader, Nebula Lord Dragon as his ace. His winning image so far is to lock his opponent's rear-guards, cutting off intercepts, locking off boosters, etc., and overwhelm his weakened opponent, which is made easier by units that gain power through Lock.
Later he refocuses his deck on Star-vader, Chaos Breaker Dragon, which, utilizing the retire characteristic of both his Narukami and Kagerō clans, lets him force his opponents to retire Locked units when they're Unlocked. This not only removes intercepts and boosts, but also builds his own defenses since he can draw a card for each retired unit.
For his fight against Ren, he changes back to the Kagerō deck utilizing his original ace card, Dragonic Overlord. However, he now possesses a new unit, one that Takuto wasn't even aware of, the Cross Ride Dragonic Overlord "The Яe-birth" and dedicates his turn entirely on Overlord as the price to restand him is to lock all five rear-guards during the main phase but also gives him a 10000 power increase for it. This give him at least two attacks regardless of whether or not his opponent guards as they have to guard two extremely powerful attacks at full strength. Adding in the reborn Dragonic Overlord Break Ride and now he comes at the opponent's units with an extra 10000 and will likely take out a rear-guard with a third attack.
In order to find out what happened to Aichi, Kai decided to use a Royal Paladin deck based on the Seekers archetype. Using Seeker, Sacred Wingal's Legion, Kai not only can send triggers back to his deck but also search for Blaster Blade Seeker to activate the Legion attack. Upon activating Legion, Kai can superior call a grade 2 unit to build his offense.
Kai later changes his deck based on Seeker, Thing Saver Dragon as his main ace card who also Legions with Blaster Blade. With it, he can superior ride another copy from the deck and Legion Mate with a Blaster Blade Seeker from the soul to have the Legion attack once more.
After losing Blaster Blade Seeker and learning that he has to be himself, Kai returns to using the Kagero clan, this time focusing on the Perdition sub-clan. This Deck's play style is to retire units in the same columns to overwhelm his opponents and using his new ace, Perdition Dragon, Vortex Dragonewt, to not only gain power when a unit is retired but also using the Legion skill to retire any 2 units and deal 1 damage to his opponent and nullifying any trigger effects in the resulting damage check, granting the Legion a starting 26000 power without any boosts or additional abilities as a result to commence his attack with.
Perdition Emperor Dragon Deck
As of Episode 192, Kai included Perdition Emperor Dragon, Dragonic Overlord the Great in his Deck, whose ability to restand allows him to dish out dangerous attacks that are sure to kill at least one of his opponent's rearguards.
During the movie, Kai uses back his Kagero deck that seems to be a mix of his 1st season deck with his 4th season deck. The deck uses a lot of old cards like Embodiment of Armor, Bahr, Dragon Knight, Nehalem, Burning Horn Dragon and his non-Perdition trigger units, the only Perdition units he used in the movie are Perdition Emperor Dragon, Dragonic Overlord the Great, Perdition Dragon, Dragonic Neoflame and Perdition Mage, Asticah.
Despite being a mix, the deck focuses on his Ace Perdition Emperor Dragon, Dragonic Overlord the Great since its effects don't require Perdition units as cost. Although not much of Kai's fights were seen it can be interpreted that Kai focuses on overwhelming the opponent with the Great's re-standing ability rather than retiring their rear-guards.
When he first fights Shion, Kai's initial deck in Vanguard G shows a heavy variety utilizing many forms of Dragonic Overlord including the G-Unit, Dragonic Overlord the Ace.
During the Star Gate Branch G Quest, Kai uses a deck similar to his Season 2 Narukami Deck which focuses on Dragonic Kaiser Vermilion and its primary support cards; the Legion unit Dragonic Kaiser Crimson which allows him to use Vermilion's Limit Break for 0 cost and the G-Unit Dragonic Kaiser Warning which gives rearguards power for each each successful hit. By combining these cards with Crownholder Dragon, he rapidly powers up his rear-guards to leave an opponent scrambling to muster a defense.
(EN): Ride the Vanguard! Burn everything in this world to ash with your apocalyptic fire! Dragonic Overlord!
(EN): Lord of Destruction rising through sacrifice... Fly and set yourself upon my enemy! Blazing Flare Dragon! Superior Ride!
(EN): Knights of the white light, please show him the way. See the King as he once was! I Ride the Vanguard! Alfred Early!
(JP): At the end of an endless quest, you arrive at final evolution! Sublimate your savage soul and show your true form! Crossride! Dragonic Overlord the End!
(EN): Harbinger of destruction, spread your ravaging flames across this battlefield! And rise from the ashes....the Overlord has reached his ultimate form!! Crossride! Dragonic Overlord the End!
(JP): Ride the Vanguard! Break the cage that seals you and descend to the field! Incarnation of the thunder! Dragonic Kaiser Vermillion!
(EN): Break through the cage that enseals you! Incarnation of Thunder! Ride! Dragonic Kaiser Vermillion!
(EN): Now I Ride the Vanguard! The time has come to break through his cage and release the Incarnation of Thunder! Dragonic Kaiser Vermillion!
(JP): Crossride the Vanguard! A silver sword on white wings! Heavenly Dragon! Dragonic Kaiser Vermillion "THE BLOOD"!
(EN): I Crossride the Vanguard! White wings and a silver sword! This is the ultimate form of Dragonic Kaiser Vermillion "THE BLOOD"!
(EN): I Ride the Vanguard! Crimson Dragon of Vengeance! Eradicator, Vowing Sword Dragon!
(JP): Powerful, ancient dragon, trace the ancestry of your form and strength and swoop down the Earth again! Break Ride! Eradicator, Dragonic Descendant!
(EN): Great Dragon of Ancient Glory. Let your presence be known! As you crash onto this battlefield! With a Breakride! Eradicator, Dragonic Descendant!
(JP): Ride the Vanguard! The black and white link, Star-vader, Infinite Zero Dragon!
(JP): Beast of war arriving from another world, seal the power of their entire army! Break Ride! Star-vader, Infinite Zero Dragon!
(EN): Slash through their hope with the pain of cursed memories! Fill this battlefield with darkness as a sign of what's to come! Breakride! Star-vader, Chaos Breaker Dragon!
(JP): Slash through everything with your cursed blade and cover the world with the darkness of death! Break ride! Star-vader, Chaos Breaker Dragon!
(JP): Roar that shatters both good and evil! Fangs that cut through light and darkness! Absolute dragon, everything grovels before you! Break Ride! Star-vader, Chaos Breaker Dragon!
(JP): Amid the flames of purgatory that reduce everything to ashes, rise from the dead again! Resurrection! Strongest flame dragon! Crossbreak ride! Dragonic Overlord "The Яe-birth"!
(JP) One ray of light, extending out into the despair of oblivion. The light is courage that connects me and my mate in the darkness. And its name...is Legion! Seek the mate!
(JP): Stand up, my avatar! The true friend within my soul... my mate! Ride the Vanguard! Blaster Blade Seeker!
(JP) The light of courage that connects me and my mate in the darkness! Seek the mate! Friendship is in this hand! Our bond is in this heart! Line up, avatar of my soul. Legion!
(JP): Lead to destruction with a flaming whirlwind! Ride! Perdition Dragon, Vortex Dragonewt!
(JP): Explosive flames of destruction that even burn away Hell! Burning Purgatory!
(JP): Seek the mate! Its roar opens a path where none exists. Those flames burn everything in this world to nothing! Stand in line, purgatory dragons. Legion!
(JP): Reduce that savage soul to ash with your swirling purgatorial flames! Trinity Crimson Flame!
(JP): Burn away all sins with the flames of purgatory! Vortex Dragonewt! Seek the mate! That scream opens up a trackless path, and those flames burn away everything in this world! Stand together, purgatorial dragons! Legion!
(JP): Ring the bell signaling the end of time, envoy from purgatory that will destroy the world! Ride the Vanguard! Perdition Imperial Dragon, Dragonic Overlord the Great!
(JP): Seek the mate! Your passionate heart bursts blindingly into flames. Appear, Dragonic Neoflame! Legion!
(JP): Calamitous flames and a burning soul! Render all walls meaningless that stand before two fiery dragons! Legion attack!
(JP): You burn in the scorching heat of purgatory, but you're resurrected again and again, emperor dragon! Feel uplifted among the flames, my avatar! Perdition Imperial Dragon, Dragonic Overlord the Great!
(JP): Seek the mate! Amid the purgatorial flames that consume everything, a new avatar of flames is born! Perdition Dragon, Dragonic Neoflame! Legion!
(JP): Seek the mate! Dragonic Kaiser Crimson, together with your mate, Vermillion, release it...Lightning of the Apocalypse! Legion!
(EN): Seek the mate! Dragonic Kaiser Crimson, fired off with your sworn comrade Vermillion...Thunder of Apocalypse! Legion!
(JP): Shed light on the vast land! Lightning frenzy that cleaves the darkness! Stride the Generation! Conquering Supreme Dragon, Dragonic Kaiser Warning!
(EN): Shed light on the universal ground! Frenzy thunder that pierces into the darkness! Generation Stride! Conquering Supreme Dragon, Dragonic Kaiser Warning!
(EN): Flames of the Apocalypse, Burn Everything in Sight! Dragonic Overlord "The Destiny"!
(JP): Flames of The Apocalypse, burn Everything to the Farthest ends of the universe! Dragonic Overlord "The Destiny"!
(EN): Wrapped in Crimson! Flames of the apocalypse, Purify Reason! Supreme Heavenly Emperor Dragon, Dragonic Overlord "The Purge"!
(JP): Clad in Crimson... The Flames of apocalypse Purge Reason! Supreme Heavenly Emperor Dragon, Dragonic Overlord "The Purge"!
