Codename: Kids Next Door (2002)

S3E12 Operation: K.A.S.T.L.E.

Numbuh 3 decides to take her younger sister Mushi on an adventure through the Rainbow Monkey Sugar Coated Castle of Love. However, their fun outing is abruptly interrupted when King Sandy and his knights launch an assault. This deranged monarch is relentless in his pursuit of marrying Numbuh 3 and threatens to obliterate the Rainbow Monkeys unless Kuki agrees to his demands.