For Sero I'd say a normal teenage voice with a slight surfer dude voice in around the mid-mid low range! He is voiced by Christopher Bevins!

Character Description:

Hanta is a very friendly person and has proven to be one of the more sociable members of Class 1-A. He can be loud and showy at times, often trying to impress his peers with his Quirk. Oftentimes, Sero is the only person to call his classmates out when they are acting crazy. He is quite humorous and often takes part in making jokes with his classmates. However, when push comes to shove, Hanta is a brave hero in training who wishes to prosper on his own while helping others do the same.