Thrym (スリュム, Suryumu?) is the boss located on the 4th (last) floor of the inverted ice pyramid dungeon known as Thrymheim in ALfheim Online as well as the boss required to be killed for The Holy Sword of the Ice Palace quest. Unlike the bosses of New Aincrad, Thrym's three large Hit Point (HP) bars are visible to players. He is the main antagonist of the Calibur side story.
Thrym was one of the Non-Player Characters (NPCs) created by the Cardinal System's «Automatic Quest Generation Function», thus the character was based on the Nordic legend of Thrym while the created character possessed a much higher degree of intelligence than usual NPCs as the NPC's core programming is connected to the language engine module, thus, instead of having a scripted response routine, Thrym is able to change his speech according to the situation to some extent. Because of this, he is much more realistic than usual NPCs.
In the original legends in Norse Mythology, Thrym was the king of the jotnar, the frost giants. In one legend, Thrym stole Thor's hammer, Mjölnir to extort the gods into giving him Freyja as his wife. However, instead, with the help of Loki, Thor disguised himself as Freyja and tricked into false marriage. After recovering his lost hammer, Thor proceeded to kill all giants attending the wedding ceremony.
In ALfheim Online, Thrym is the king of the frost giant tribe of Evil Gods. He once turned himself into a wolf and infiltrated Jötunheimr and there he stole the «Holy Sword Excalibur» and threw it into Urðr's spring at the center of Jötunheimr. The sword severed the roots of the World Tree that were rooted in the spring and thus, at that moment, Jötunheimr lost the blessings of the World Tree and turned into a frozen wasteland. As the roots of the tree retracted towards the canopy of Jötunheimr, it carried the frozen water of the spring with it, later forming an ice dungeon that was named Thrymheim.
Thrym took up control of Thrymheim and restructured it into his fortress, from which he began ruling over Jötunheimr and sent his subordinates, the frost giants to capture and imprison the native inhabitants of Jötunheimr, the rock giants, while massacring the beasts living within Jötunheimr to cripple the power of Urðr and her sisters, as they were the only ones preventing his castle from breaching the canopy of Jötunheimr to invade the fairy world of Alfheim, enclosing it in ice and snow. Thrym's ultimate motive is to reach the top of the World Tree to obtain the «Golden Apple» that exists there. Eventually, furious about not being able to wipe out the beast-type Evil Gods, he decided to enlist the help of the fairies, promising them Excalibur as a reward for their help, however, in case he succeeded, he would give the «Fake Sword Caliburn» as a reward, as the real Excalibur is the only thing that is keeping the World Tree from re-growing its roots back into Urðr's spring.
In the non-canon slight failure version of Calibur, it was revealed that Thrym's quest was triggered by Marinca, who activated the Cardinal System's quest generation function and forgot to disable it afterwards, thus Cardinal System began the scenario of Thrym enlisting the help of fairies.
Thrym is a humanoid giant who is at least fifteen meters tall, has dull-blue skin like lead. The giant had brown fur coiling around his arms and legs and wears a plate armour, a single piece of which is the size of a small boat, on his waist. The upper part of his body is bare, revealing prosperous muscle that looks as if it could repel any weapons directed at it. The giant also has a blue beard that reaches his chest, has a long mustache, blue and bleak eyes and wears a gold crown on his forehead.
Thrym's initial attacks patterns include punches with both fists, three continuous stompings using the right foot and then the summoning of twelve ice dwarf soldiers from the floor.
After the first HP bar is depleted, the boss's attack patterns change. One of his new attacks include a wide-area breath attack that first begins sucking up the air around him and then unleashing a wide conal diamond dust that freezes up all players caught in the attack's range. This attack is then followed by a furious stomp with the right leg that greatly decreases the HP of the players.
The boss's weak point is his upper body, around the area of his beard, however, due to the giant's size, the weak point can only be reached by ranged attacks.
Due to the urgency of the quest, Kirito's party did not make any special preparations for the boss battle, aside from bringing a decent supply of potions as well as repairing weapons before taking up the quest.
The initial strategy for the battle was to listen to Yui's instructions to figure out the boss's attack patterns and avoid the boss's attacks, while Sinon took care of the minions from the back and then to use Sword Skills against the boss, as his fur had high physical resistance. Meanwhile, Freyja provided additional offensive power with her thunder magic.
As Thrym began unleashing his breath attack, Asuna had to begin pre-chanting high-level healing spells to quickly recover the lost HP of the vanguards, while Sinon distracted the boss by attacking its weak point to buy time for the vanguards to heal.
In the middle of the battle, a subroutine of the quest activated and Freyja asked for help in finding her lost treasure, a hammer, within the room. After using «Lightning Fall» to find the item while Klein and Leafa backed up Sinon to distract the boss, Kirito located the hammer and threw it towards Freyja. At that moment, Freyja started growing in size and changed from a beautiful lady into a giant aged man who was revealed to be Thor.
Now in his true form, Thor rushed in to attack Thrym for stealing his hammer, while Thrym created an ice battle axe with his breath to counter the attack. While the two giants were busy exchanging blows with each other, all the fairies attacked in full force with their Sword Skills to help Thor bring down Thrym. In the end, Thor delivered the final blow by slamming the hammer in his right hand at Thrym's head.
- In the original myth, Thrym did not invade Jötunheimr, as it was already the homeland of the giants. Thrymheim was actually the abode of Þjazi.
- Dubbed SII Episode 16 Credits