Hybrid x Heart Magias Academy Ataraxia, Vol. 1 (manga)

Invaders from another world are attacking the Earth, and humanity's only hope lies in special armors called Hybrid Heart Gears, or HHGs. Hida Kizuna might seem unexceptional, but he has a skill that can turn the tide of battle--by getting female HHG users hot and bothered, he can replenish their energy!