"Repeating crossbow cherished by the weapon craftsman Eidas. Its elaborate design makes it closer to a work of art than a weapon. Intricate mechanism makes heavy damage possible through triple-shot firing of bolts. but in fact each bolt inflicts less damage."-Avelyn
The Avelyn is apparently an invention of his, it fires three bolts in a row quickly. Ask yourself, how many bolts do the traps in sens fire at you? Now, this isn't one of those "Sen is Eidas!" threads. I'm just trying to discuss the idea that he could have had a hand in at least designing that one type of trap.
Consider that Sen's is full of Serpent People as well, which the Duke's also contains. The Duke's being the location with Avelyn in it, as well as the remnants of intricate machinery.
I don't believe this has been discussed before, but if so just point me in the direction of the thread.