The character you are talking about is Honma Meiko.

The heroine of this work. A fair and petite girl. Naive, super peaceful mascot in Busters. Have a unique way of speaking. Although my muscles are a little weak, I still understand some things. Because I quarreled with Rentai in my childhood, I was accidentally killed. Ten years later, I reappeared in front of Rentai as an adult, knowing that I was dead. Only Honma Meiko (the soul, only Rentai can see) died in his childhood.

attached drawing