Park Jin shows Yul the blue mark on Naksu's body
At Songrim, the leader teaches Yul how a soul leaving its body leaves a blue bruise, and they find a bird whistle on the dead assassin.

Every Alchemy of Souls moment featuring Park Jin, in story order. Played by Yu Jun-sang.
114 moments · 4h 21m · by Favseen
Moments 1–30 of 114
At Songrim, the leader teaches Yul how a soul leaving its body leaves a blue bruise, and they find a bird whistle on the dead assassin.
Dang-gu rushes to his uncle with rumors about Naksu, gets scolded for hanging around bars, and reveals Uk has been sent to train with a monk.
Unable to draw his father's sword because of the spell on him, Uk is told no one will open his gate of energy, and vows to find a master himself.
Masked intruders break into Songrim, the Training Center burns, Jeongjingak is emptied, and Mu-deok realizes her old master sent them.
Naksu's body is gone and a spy is suspected; Uk teases Mu-deok while the others discuss how soul shifters pick similar bodies.
Everyone in Songrim is gathered and locked in while Jin Cho-yeon brings Gwigu, the Jin family's ghost dog that sniffs out sorcery.
The Four Seasons are together again for the first time since Uk and Cho-yeon called off their wedding, and it shows.
Mu-deok learns he broke the pottery to save her; the Songrim leader confronts Uk and forbids him from moving or speaking.
The king considers promoting Jin Mu for killing Naksu's men; Songrim objects, and Jin Mu asks to burn Naksu's body and keep her sword.
Pressed about the infant, Jang Gang says sealing his power is the only way the boy lives, and calls him the son of a dead man.
Uk tells the Songrim leader he poisoned himself and his maid only obeyed, then refuses treatment unless Mu-deok is treated too.
Heo Yeom admits he opened Uk's gate and gave him extra energy to recover; Park Jin insists he take it back to keep Uk far behind.
Heo Yeom demands the wine hidden in Park Jin's room, teases him about never getting over Do-hwa, and finds the bottle already empty.
Over stolen wine, Dang-gu and Yul find Mu-deok suspicious for faking blindness, then Yul abandons Dang-gu as his uncle arrives.
Maidservant Kim raises the rumor that Park Jin is Uk's father; he brings up her acorn jelly for Jang Gang, and both admit to old, unhealed loves.
Park Jin remembers being told Uk's father was the late king, and that a destined king would be seen as treason, so Uk must seem ordinary.
Uk asks to join Songrim and offers Naksu's sword; instead he is banished and, for losing the Spirit Plaque, sentenced to a hundred lashes.
After 99 lashes Uk refuses to leave, demands the leader deliver the last one himself, then has Mu-deok take the sword.
A plea to let Uk return is shut down; over a soul shifter's petrified victim, the Songrim leader explains the alchemy of souls needs Hwansu mastery.
Uk shows the Songrim leader he can now draw his father's sword and begs to be taken in, but unbound, his arm cannot hold the blade.
Cho-yeon brags that Uk beat the Crown Prince, but the leader hears Uk threatened the Prince and orders him locked up as dangerous.
Uk vows to become Gwanju like his father; Park Jin tells him he is not Jang Gang's son and should stop dreaming.
Nursing a wound he chose not to dodge, Park Jin muses about claiming to be his father; Maid Kim's jab about his looks turns into a grudging truce.
Royal guards come for Uk after the duel challenge; warned he could lose his arm or life, he slips away to Sari Village with Mu-deok.
At a Unanimous Assembly, mages who once taught Uk propose stripping his powers; Songrim accepts the royal duel instead.
The soul shifter was a Cheonbugwan star recorder, so Jeongjingak mages search the office and ask to see its secret room.
Cho-yeon's mother offers to block the King's order with the Jin family plaque, if Uk marries Cho-yeon; Cho-yeon says she still wants him.
Debating the Jin marriage, an elder admits he once left his master for love; then an intruder breaks the barrier and Heo Yeom greets his master.
Master Lee suspects Cheonbugwan, reins in Heo Yeom, teases grown-up Park Jin, and reveals he took the dog Gwigu to hunt soul shifters.
Yul tells the Songrim leader of a girl hiding in Danhyanggok whose father wrote down the stars, and learns of a recorder killed by the four families.