Unlike a regular Frost and despite his appearance, King Frost is ruthless and his power unyielding. He is not friendly and likes to exercise his status as a king to even go so far as to consider his summoners as his subjects as well.
King Frost can only be acquired through a triple fusion of three different Jack Frost variations. He regularly appears as an event boss during the Christmas period. His crown, padlock, and wand all appear as player equipment.
"Heeeeee! Hoooooooo! Hee! Ho! Hee! Ho! Hee-ho Hee-hoo! I'm the boss, King Frost! Of course I'm the boss! I'm the King! All I have to do is breathe and freeze everything! Hee-Ho! You want to be frozen, too? Ho-kay, I'll do it! Heeeeee! Hoooooo! Hee-ho!"
—King Frost, Devil Summoner: Soul Hackers
King Frost appears in the first Room of Trials at the Corridor of Time. Defeating him is necessary to obtain the Bronze Manji.
King Frost first appeared in Episode 12. Yu Narukami summoned him as one of his attempts to attack Shadow Mitsuo. King Frost was used to shoot a blast of Bufula at Shadow Mitsuo. Unfortunately, this attack was blocked and Yu was forced to use another persona. King Frost is also the Persona that represents the bond between Yu and Kanji.
Replacing Hel as the new Tyrant of the Ice Expanse and leader of the Frost Clan, King Frost is the more benevolent leader of the tribe. Seeking to aid Masaki Kuzuha when he asks for a cure to the Dark Slumber, he has the doctor Dian Cecht give it to Takaharu Ougi. Later he will be taken hostage by the angels of Tenkai, who seek to turn his castle into the stronghold they will use to invade all of the Expanse. He is grateful to Masaki when he frees him.
Known as King Icy, he rules over Frostville and the Ice Temple. In Dark Version he is taken hostage by the Imperium's Harborim, but is saved by Akira. King Icy is obtained by ranking up a Jack Frost ten times through fusing ten consecutive Jack Frosts together. Since ranking up is not available in Light Version, the only way for Jin to obtain a King Frost is through link trade. After beating the game King Icy will move from his throne so Akira and Jin can access Lucifer Frost, who the King can sense.
King Icy can perform the Ice combo Blizzard with J. Frost and Freeze wave with Icy Ace.
"This is the King's castle, HO. The King decides the HEE code. Those who disobey are sentenced to HEE HO death."
—King Frost before his boss battle
After Serph and company defeat Mick the Slug, King Frost takes the opportunity to reoccupy Coordinate 136 with his own demons. Upon reentering the castle, Serph encounters two Pyro Jacks fiddling away at a treasure chest. Having tried their luck, the Pyro Jacks turn to the party to find a suitable key within the castle promising that the treasure within is for Embryon to keep. It was, however, a lie.
After the party retrieves the correct key, the Pyro Jacks run off with the treasure to present it to their king. To get back their spoils, the party ventures to the top of the tower to find King Frost sitting on the platform above the bed in the Princess' Bedchamber. Declaring that all possessions belong to him, King Frost decides to smite the party for their insolence. After a harsh struggle combined with the forces of his minion Jack Frosts, the party defeats King Frost and obtains the Ice Crystal, which unlocks the King Mantra.
King Frost summons a more powerful variant of Jack Frost, created by apparently fusing two regular Jack Frosts.
Upon defeating him, players can obtain the Hee-Ho Karma ring in the sequel, which grants the wearer immunity to Ice-based attacks.
King Frost is one of the first few bosses in the game. He has taken up residence in a spring within the Fairy Forest to hope to get the others to help him find a treasure, according to a demon from the Divine Powers. This causes Napaea to send for help, leading the protagonist to him.
King Frost's battle introduces two things - first, the Assist Gauge that causes all battle partners to team up and pile on an enemy, thereby skipping their turn; also, that several moves have Smirk-related additional effects and bosses are not afraid to use them. While King Frost's first turn will always be skipped due to the Assist Gauge automatically filling at the start of the battle, this is only a mere reprieve before he commences attacking.
King Frost has a +4 bonus to his ice skills, making it very difficult to outlast his attacks without ice resistance. The issue behind the fight is his use of Smile Charge at the end of his turns which will grant him a guaranteed Smirk. Not only will it neutralize his weakness to fire and drag out the battle, but it also causes his signature move, King Bufula, to land a critical hit on the whole party while lowering their defense.
One of the best demons to bring to the fight is Napaea herself - she eventually resists ice while innately learning Agi without any penalty to strike King Frost's weakness. Navarre is an excellent battle partner option as he gets access to Rakukaja to offset the additional effects of King Bufula. Bring your hardest hitters, as the battle will quickly degenerate into a damage race between the boss and the party, unless King Frost randomly wastes his Smirk on a normal Bufula.
His battle theme in Devil Summoner: Soul Hackers is a slightly updated version of Dr. Thrill's theme.
King Frost is one of the few demons who uses a design originating from DemiKids on another franchise, and seems to be the de-facto design for any time a game uses models, most likely owing to the simpler design compared to the original King Frost which is used in games that use sprites.