Tween Kidd coming to the realization he has to get stronger; that his friend will gladly destroy himself for Kidd if Kidd doesn't stop him- a heavy realization for any kid, especially one as proud as Kidd. Childhood is ending, a growth spurt just around the corner and soon he'll be big enough he wont ever have to watch Killer take a hit meant for him ever again.
Not that Killer wont try anyway