For most of the game, Yakra XIII disguised himself as King Guardia XXXIII's Chancellor. He would hire Fiends to impersonated Royal Guards for the Prison Towers and constructs the Dragon Tank. After Crono and his friends return to the present, Yakra XIII states that Crono had kidnapped Marle and puts him on trial in the castle's courtroom. Crono is charged with the abduction of Princess Nadia. People are brought in from Leene Square who interacted with Crono and Marle as well as people hired by the Yakra XIII to falsely testify against Crono. When Crono is taken to the Prison Towers, even if he has been pronounced innocent, Yakra XIII tells the ward that he has been found guilty and will be executed in three days.
Yakra XIII sends the Dragon Tank to kill Crono when he escapes, but he defeats it with the help of Lucca. The Fiend then chases them into Guardia Forest intending to execute the death sentence himself. However, they escape through a Gate.
Later, when Marle enters the castle, he revealed the death of her mother, Queen Aliza, as being the result of her father's negligence. She desperately asked to see King Guardia XXXIII one last time, but the Chancellor refused to grant the audience, saying that the King could not leave his work unattended.
Eventually, the King is put on trial. Yakra XIII prosecutes the King for allegedly selling the royal heirloom, the Rainbow Shell when a falsified ancestral will proclaims the shell should have been unveiled at the Moonlight Parade. Marle enters the courtroom, and the King tells her that he is being framed by the Chancellor. The Chancellor asks for proof, saying that if the King has not sold the heirloom, then it should be somewhere in the castle. Shortly after, Marle is kicked out of the courtroom. Marle and two others decide to search the castle for the Rainbow Shell. Meanwhile, the King's trial continues, the false Chancellor bringing forward people to falsely testify against the King. The party finds the Rainbow Shell within the castle meanwhile Marle breaks into the courtroom by breaking through the stained glass mural by jumping behind the Judge's seat.
Once the Chancellor says they are too late; a guilty verdict had been reached. At this time, Marle reveals a shard from the Rainbow Shell with the King fleeing, as the Chancellor finally reveals his true colors while transforming into Yakra XIII. Inflamed with rage from his late ancestor, Yakra's humiliation for failing to capture Queen Leene, he attacks the party. After he is defeated, he drops a key that opens the chest which the real Chancellor is locked in.
Boss Battle Strategy
He is quite hard. He will attack with Chaos that will confuse your characters if they have no protection against status ailments. And, when you damaged him by 10000 he will begin attacking you with much stronger attacks. All you have to do is to have Marle be the healer because she has a complete set of Curative Magic, then have the other 2 characters attack Yakra with their most powerful Tech. Beware also because after you beat him he’ll unleash his final attack that damages all your characters by 200+. So keep your HPs above 300 as much as possible.