Midori Arai  

Breathless

The character you're referring to is known as "Sacrifice Unit" or "Stronger One." He plays a crucial role in providing strength and encouragement to his partner, who is referred to as "AIS Sacrifice." This character's name appears on the palms of one hand. Despite being sent back home to finish their own schooling after they were ordered not to retrieve Ritsuka, they remain close and do not like to be separated from each other.