Before Hajime is experimented on, he would be very nervous when it comes to dating. He is very quiet about it at first and can get easily flustered if you were to hold his hand or kiss him on his cheek. 

When he gets used to holding hands, he'll gently stroke the back of your hand in a loving way...

As for kissing and hugging, once he gets used to that stuff he'll get addicted to the point where he constantly wants to hold you.

Hajime drinks his Respect-Women juice (despite what Mahiro has to say about it) and will give you forehead kisses and little eyelid kisses too.

He is a little anxious about how good he is for you, say he might down himself saying he may not be the best boyfriend or something like that. He does need reassurance here and there but over all is sweet and gentle with his partner.