"Shiro." Very seriously and patiently, here. "He's part of me. Why would he hate you?" While...technically true, Marshmallow is also part Deerington itself, William, so there's a lot to work with here.

Also Shiro is very clear, Will is just...well, he's inclined not to always believe the best. Like now, eyes widening, looking up at Shiro like the idea's just now made sense to him. Because it has. Honestly, this kid.

"You...really? You are?"