Gemini is the alias of two sisters with an unusual predicament. Moira and Penelope found themselves tethered to a pocket dimension that exists outside of the timestream. Now only one can exist in the real world at a time.
Gemini is a hybrid tank with good peel potential, and both play around the theme of health pools and taunting. Penelope can give everyone a second more under fire before dying by redirecting some of that damage to herself. Lucky for her, her main weapon increases her maximum health so she can endure the focus fire. Penelope's role is supportive in nature, whereas Moira is more active.
Moira's kit is based around the berserker playstyle. The lower her health, the faster she moves and attacks. Balancing these two might be a mighty task, but I think having them play as a tagteam duo seems really fun.