Styx

Styx is an original fictional character.

Background
Sesi Adesina was lucky enough to have been born in Wakanda, one of only a few countries that refused to adopt an American-style Registration Act outlawing mutations. When her own mutation surfaced at the age of 14, she was sheltered rather than persecuted, and promised an education that would enable her to one day control and even master her unique power.

But Sesi's power was not so easy to master. Her innate connection to the Darkforce Dimension seemed at odds with her sweet, gentle, and positive disposition, and even after a year of training she could barely muster the conjuration of a whisp of dusty smoke. Her parents pleaded with Unity for assistance in Sesi's training, but Anole, their leader, refused. Unity was not the X-Men, he made that perfectly clear; moreover, in his view, the last thing the world needed was more Darkforce.

Sesi and her family were about to give up on her training when a potential teacher unexpectedly came to them. Wither, leader of the most recent incarnation of The Brotherhood of Mutants arrived in Wakanda and offered Sesi an opportunity to learn to master her powers under his tutelage. After some deliberation she refused his offer, but Wither would not take no for an answer. A fight ensued, which quickly got out of hand as a team from Unity and even the Black Panther herself got involved.

Amid the chaos and violence, Sesi's powers suddenly surged wildly out of control. Viscous black liquid - a rare and powerful manifestation of pure Darkforce - bubbled up from the earth itself and ran through the streets like a river, pulling those it touched down into the Darkforce Dimension. Terrified, Sesi struggled to regain control, and Wither chose that moment to restate his offer to help her master her powers. A desperate Sesi accepted.

Together with the Brotherhood, Sesi and Wither disappeared through the Darkforce Dimension. Some of the Wakandan guard who had been sucked into the black waters managed to crawl their way back out before the river receeded back into the earth; at least a dozen did not, and were never heard from again.

Sesi is now believed to be a fully-fledged member of the Brotherhood, going by the codename "Styx".

Powers and Abilities
Sesi is a human mutant, and though the the relative potential of her mutation is unknown, she has already demonstrated power at what is likely Alpha-level or higher. Sesi's power over the Darkforce Dimension is so potent that she can channel pure Darkforce in a form so solid that it resembles a heavy liquid - a rare and impressive feat even among Darkforce users. She has exhibited the ability to draw people into the life-draining dimension itself, and can effectively teleport herself and others unknown distances by using it as an intermediary location.

Little else is known about her abilities, or what, if anything, she may have learned from her time with the Brotherhood over the last three years.