Hajime is your ultimate lady's valet (not a butler, as he says repeatedly), serving as Naname Nanami's bodyguard, tutor, and general servant.  He and his sister, Hana were brought to the Naname Manor as children after their parents' death to live as servants by the head of the Yuuzenji Family at the time (the Yuuzenji are one of seven cadet branches of the Naname Family).  He earned Nanami's trust and became her ultimate ally, protecting her from attempts to forcefully betroth her to members of the cadet families through an antiquated duel system, where he essentially beat the crap out of the suitors in question.  Unfortunately, in the process he also indebted himself to Tsurumi, which is one of the causes of the mess you see unfolding from the very beginning of the story.

He is capable, both in scholarly pursuits and martial arts, as well as in terms of etiquette and service.  He is also well-educated in financial pursuits, as he was intended from the very beginning to double as Nanami's aide when she took over the Naname Conglomerate. 

Unfortunately, as a result of his need to protect Nanami from Tsurumi as well as from various other elements both in and outside the family, he has developed a somewhat narrow view of the world... essentially, the people that he loves are all that matter to him, and he would gladly toss the rest of the world (including himself) into a bonfire if that would keep them safe.  This results in him fundamentally misunderstanding the people he loves on several levels and biting off more than he can chew on more than one occasion. 

He has a potential for ruthlessness that almost equals that of Tsurumi, and he is the type that honestly doesn't care if his soul is stained black if that is what it takes to save Nanami and his sister Hana.