We know he builds up aura to create a shield and an arrow, which makes a rumbling noise that can be heard throughout the first tier of the black whale. To do this he needs to be surrounded with his followers. But here before we were introduced to the limits of his ability he builds up aura while Sumidori (the swapped in follower in Shikaku's body) approaches Luzurus's room. Why though? Sumidori approaches alone and kills himself. No one else is in the long hallway beside him.

At the same time Luzurus's bodyguard, Rice, falls backwards. INITIALLY! I assumed that the arrow had come from a front angle, but now I'm sure it came from the left, directly.

The first time we see Halkenburg use Grimal Les Dissonances he shoots pretty straightforwardly down a hall and through the soldier (Shikaku's) shield, but not through any walls. That plus the unknown parameters of his abilities at the time are why initially I didn't think he was doing anything here other than a test. But later when Halkenburg takes down Balsamilco he shoots him while hes in the middle of a hallway without Halkenburg on either side.

He knows exactly where Balsamilco is and aims through the wall. Now returning to Rice. At the time when Sumidori/Shikaku shoots himself I assume Sumidori's soul returns to his body very quickly, if not instantly. But when he wakes up Halkenburg is sitting directly in front of him in what looks to be his room, meaning at the time when there was a rumble to build up energy, Halkenburg and his followers never left his room.

How did Halkenburg shoot Rice without leaving his room? How did he know where to shoot? WELL! Halkenburg is the 9th prince, Luzurus is the 7th prince. Their rooms are right next to eachother, and every single room has the same layout.

so Halkenburg would know exactly where to shoot IF SOMEONE WAS ANSWERING THE PHONE.

Do you all feel like if Luz hears great music in a public place, he would just be like :