Soul Seeker is a Gold Shadow that is fought for the request, Investigate the Evil Spirit Club that is available once the player ventures into Inaba Pride Exhibit Night 3, replacing Kind Doctor. The reward for completing the request is the All-Around Badge, which grants its wearer +50 to HP and SP and +5 to all stats. The Black Orb, which Elizabeth dubs the Sphere of the Underworld, is found behind it. The Monitor Gold it drops allows Theodore to create the Paralysis Knife for Yosuke and Koromaru and Paralysis Buster for Aigis, Poison Bullet for Zen, and Eternal Blade for Mitsuru, which grant a 15% chance of Paralysis, 15% chance of Poison, and 10% chance of instant kill, respectively.
The Soul Seeker is a rare Shadow appearing in the lower floors of the fourth labyrinth. It is protected by an Affinity Barrier until it is at low health and the last enemy standing. Attacking it while it has the Barrier up will cause it to drop money.
The Soul Seeker "is watching" when it's about to change its attack patterns. It will start with normal attacks, Evil Smile and Maragion till 50% HP. Past that, it starts using Agidyne and Stone Mist, and then Maragidyne and Mamudoon for the final bit of HP.
Perhaps the most worrying feature of this boss is its Mamudoon attack, which is likely to completely wipe out a party that doesn't resist it. Stone Mist can also be a problem to those without Me Patra or similar ailment-curing items, and the Curse-inducing Evil Smile exploits its low Defense to heavily damage your hardest hitters. However, successfully getting a Magic Bind on it or putting it in Panic will almost completely neuter this enemy, making it unable to use any of its main attacks and having to try damage the party with its underwhelming normal attack.
Otherwise, bring party members resistant to Fire and/or Dark. The P4 Hero is almost mandated for this fight as he is guaranteed to survive a Mamudoon and is free to revive the unlucky party members. Those on the Persona 3 path, whose protagonist is weak to Dark, will have to suffice with either a Resist Dark effect on the protagonist or stocking up on Homunculus to avoid Mamudoon deaths. Koromaru's resistance to both of this boss's attacks also make him a great party member to bring to the fight.
Those who find this fight difficult can utilize the free DLC Sub-PersonaOrpheus Telos; its skills Healing Harp and Absorb Fire can make this fight much easier. Healing Harp cures all ailments at the end of each turn, which makes the Soul Seeker's Stone Mist little more than a nuisance. Once Soul Seeker reaches critical HP, if Opheus Telos (with Absorb Fire) is equipped to the P4 Hero he will be unkillable, allowing the player to leisurely whittle down the rest of its health with normal attacks if necessary.