While Alphinaud and Hien discuss how to proceed, you speak with Alisaie.
This quest is available if you have completed the quest Storm on the Horizon.
Starting the Quest
Talk to Alisaie in the Doman Enclave to begin the quest. There will be a cutscene.
Speak with Asahi
You can either teleport to the House of the Fierce and go west to where the orange arrow is pointing in the minimap, or use the Doman Enclave Aetheryte or an Aethernet Shard to go to The One River, then go north to where the orange arrow is pointing in the minimap. Talk to Asahi to proceed.
Speak with Asahi Again
Go north to where the orange arrow is pointing in the minimap. Talk to Asahi.
Speak with Asahi Once More
Go south to where the orange arrow is pointing in the minimap. There will be a glow around Asahi, indicating an instanced battle. Check on him and there will be a cutscene, and then the battle will ensue.
Solo Duty: His Forgotten Home
Focus your attacks on the Slickshell Captain, then when he is defeated, attack any Softshells of the Red that attack Isse, and watch for any new enemies to appear. You can try to bring the enemies near Yugiri and Asahi so the enemies will be hit by their attacks.
After the battle, there will be a cutscene.
Speak with Asahi Once More, Again
Talk to Asahi to complete the quest.
Next Main Scenario Quest
After you complete the quest, talk to Asahi to accept the next quest: A Guilty Conscience.