Giselle Gewelle is a Quincy and a member of the Wandenreich's Sternritter with the designation "Z."
Giselle has long, dark-colored hair extending down to the lower back, with two strands sticking up like antennae. His attire is a variation of the Sternritter's typical white uniform, consisting of a trench coat with long sleeves, white shoes, and black leggings.
His power is called The Zombie. Anyone who has Giselle's blood splattered on them falls under his control, effectively becoming a "corpse" and doing whatever Giselle orders them to do. This aspect of the ability does not work on fellow Quincy unless they have already died. Giselle can use his power to heal comrades by using the flesh of the deceased to replace their own.
He also plays a pivotal role in Wandenreich's second invasion. He faces off against Ikkaku and Yumichika, the latter of which questions whether Giselle is actually a male despite how he refers to himself as a woman, which enrages Giselle several times throughout their fight. Giselle uses his zombies to push them back, but Mayuri arrives with his own zombies and launches a counter attack. After Yhwach uses his Auswählen, Giselle betrays him along with Bazz B and Liltotto. They are all defeated, though in the 'Can't Fear Your Own World' novels Giselle and Liltotto were revealed to have been rescued by Haschwalth's unnamed attendant.
Despite the feminine look to the character, as well as some of his dialogue, Tite Kubo confirmed that Giselle is a man in his website's Q&A #288.