A straight-laced detective,Espio is serious, practical, intelligent and wise. He has a militaristic discipline despite being quiet and laid-back. Espio is additionally portrayed as being stubborn, opinionated and self-obsessed. Despite this, he has an excellent drive to all that he does and flourishes off of peril, getting himself into threatening situations to flex and polish his ninja skills, and, due to his extensive training, he can confront these troubles head-on unconcerned by danger.

Espio values his freedom more than anything else. This is due to his reserved demeanor, which hides a burning sense of justice and a refusal to let evil have its way.

You can base this interpretation on his past voices. If not, something witty, serious but capable of being petty childish.