*NOTE: Recommended level is 57.
Obtained: After Yashiro reaches Stage Rank 12 and you progress far enough in Chapter 6 (after you enter the Cosmic Egg Idolasphere), a new side story will become available. Read the Topic then travel to Cafe Seiren in Shibuya and speak with Yashiro.
After the cutscene, head to the Area of Memories to trigger a brief cutscene then travel to the Third Relief to face off against Lon’qu (level 59). Lon’qu does frost and sword attacks. His weaknesses are Spear and Fire. Lon’qu resists Wind and is null to Frost, Axe and the Red Skull. Lastly, he is neutral to Sword, Bow and Electric. Defeat him to trigger a cutscene.
After the cutscene, head on over to Bloom Palace to unlock Yashiro’s new Radiant Skill called Door of Denouement.