Setting on your expendition for the Crystal that's located in the Hadal Blacksite because Urbanshade told you to get it, you had to enter a submarine to descend into the Hadal Blacksite.

That was, before you came to Sebastian's makeshift shop.

He was there, standing as he played the electric guitar with two of his arms, his third hanging limply, occasionally joining to play some more tunes as he played the Electric Guitar.

You sat there, listening carefully. It sounded nice.