Ser Derrin has prominent cheekbones and brow, and short cropped golden hair. When his sister married Lord Mallister, Ser Derrin followed, finding service in the more prominent and militant seat of Seaguard. Though talented, he has yet to rise to a position of command, as Lord Mallister elevates men born and raised within his own keep.

He is the youngest of six siblings, being brother to Lady Alianna Darry, Lady Catryn Mallister, and Lady Frey.