One of the first NPCs you'll meet when you enter Roundtable Hold, Diallos is a tricky guy to follow around. His questline requires traveling to some very specific places that are off the beaten path, and if you don't like to explore he may disappear from your game altogether. Let's follow his progress.

Step 1: Meet Diallos

Your first meeting with Diallos will be when you initially reach Roundtable Hold. He's standing in the main room, near the door to the balcony overlooking the ground floor, and will greet you warmly. Diallos will ask if you know the whereabouts of his servant, Lanya, who is quite free-spirited and flighty. You don't know, so you'll have to keep an eye out for her.

Step 2: Travel to Academy Gate Town

Diallos will leave Roundtable Hold after your first conversation with him. You'll find him next at Liurnia of the Lakes, in the Academy Gate Town that sits at the entrance of the Academy of Raya Lucaria. Head north through the eastern side of Liurnia of the Lakes and you'll find the Academy Gate Town quite easily. Diallos is standing on a sunken rooftop in the north of the town. You can find him by checking the spot on the map just to the right of the Academy Gate Town icon.

Diallos has found Lanya before you, and unfortunately, she's dead. Diallos knows who's responsible, as well, and vows revenge.

Step 3: Travel to Volcano Manor

Head back to Roundtable Hold and you'll find Diallos in the central room again. Speak to him and he'll say that the 'recusants' who killed Lanya tried to recruit him into their service. He'll reveal that they're based in Volcano Manor, found on Mt. Gelmir. He'll leave Roundtable Hold again after delivering this message.

There are three ways to reach Volcano Manor:
  • Be recruited yourself. Rya, the 'talent scout' of Volcano Manor, is in a small pavilion near the Scenic Isle Site of Grace in Liurnia of the Lakes. Complete a task for her, then meet her at either the Grand Lift of Dectus (if you used it) or the Lux Ruins (if you went through the Ruin-Strewn Precipice) on the Altus Plateau. She'll teleport you straight to Volcano Manor.
  • Be teleported there by Iron Virgin. Patches will tell you that a specific Iron Virgin shunts people it traps straight to the Erdtree. This is a lie, of course, and if you're caught by this particular Iron Virgin it will send you to a back section of Volcano Manor. Once you escape you'll be on the Altus Plateau, and can walk or ride the rest of the way. The Iron Virgin in question is in the Academy of Raya Lucaria, at the bottom of a huge lift system. You'll need to let it grab and kill you.
  • Walk. Make your way to the Altus Plateau and enter Mt. Gelmir via a valley near the Wyndham Ruins. You'll find a twisting path near the rear of Fort Laiedd that will, after some time, take you up to Volcano Manor. You'll need to Spirit Spring up to the Full Grown Fallingstar Beast's battle arena and jump off to the right to make the final leg of the trip. (You'll also need to make this trip if you used the Iron Virgin to reach this area.)
Speak to Tanith, the mistress of Volcano Manor, and agree to enter her service. She'll give you a Drawing-Room Key that will allow you to unlock many of the doors in the nearby hallway. Diallos is in the larger room on the left, along with Recusant Bernhal and Rya. Exhaust his dialogue here and you'll see he's a rather... persuadable man.

Diallos will come and go. Speak to him again after killing another mark, either for Tanith or Patches, and he'll bemoan his own foolishness. Make up your mind, guy.

Step 4: Travel to Jarburg

To meet Diallos again you'll next need to make a trip to Jarburg. The home of the Living Jars of Elden Ring, Jarburg is located next to the Carian Study Hall in Liurnia of the Lakes. To reach Jarburg you'll need to get onto the eastern cliffs of Liurnia of the Lakes and ride north until you reach the Carian Study Hall's upper walls. Look along the cliffs just south of the Study Hall and you'll see gravestones jutting out of the rock. You can use these to hop down to Jarburg. Activate the Site of Grace so you don't need to make a long trip to get here again.

Once in Jarburg you need to speak to Jar-Bairn. He's a little jar sitting on the steps of one of the houses nearest to the Site of Grace. Jar-Bairn will start off by asking if you'll be the new 'Potentate' of Jarburg, though he dismisses you as a candidate pretty quickly. Keep talking until he runs out of dialogue, then refresh the area and speak to him again. You'll have to keep doing this until Jar-Bairn mentions the coming of a new Potentate, who is, of course, Diallos.

You'll find Diallos in a half-ruined house, cleaning another small jar. He seems satisfied with his new lot in life, and will stay here for quite some time. To progress past this you'll either need to wander off to other parts of the game and come back later, or just go to the Site of Grace and Pass Time several times. You'll know you're ready to proceed once you can no longer see Jar-Bairn sitting on the steps.

You'll find Diallos laying in the middle of Jarburg, having fought to defend the village from attack by poachers. He'll ask you whether he was successful in defending the jars. You can say whatever you like. He'll die shortly thereafter. Rest at the Site of Grace once to move Jar-Bairn over to Diallos, speak to him - he sounds different - then rest at the Site of Grace again. Diallos will be gone, leaving behind Diallos's Mask, Hoslow's Petal Whip, and a Numen's Rune.