Shou Matsubara (known as Sam in the English dub) is Buttercup and Dave's younger brother.

He is the third child and second son, of Mituko Matsubara and The Masked Wonder, and has appeared in several episodes of The Powerpuff Girls Z. The first one was And Then There Were Three when his voice was heard only. His next appearance, in person, was then in All Ken Wants for Christmas (Episode 26), and then again in Trading Faces (Episode 40), Buttercup's New Moves (Episode 44), and a cameo in The Final Battle (Episode 52). He was mentioned in The Happy Thought Blaster (Episode 49), as well.