Introducing Hiki, Yukiko's little bother from a different father, which is the mother's current boyfriend.
His name is Daiki, but when he was learning to talk, he couldn't say his own name right and used to say Hiki(=toad) instead, hence the nickname. From then on, Yukko's bought him a ton of frog-related stuff.
He is a ball of pure joy! Always happy about doing stuff with her sister, wanting to learn as many new things as possible, willing to go all over the world with Yukiko. He enjoys being MonKei's partner in crime when it comes to pranking Yukiko, and he loves piggy rides on Kuro's shoulders. He likes to make Ame mad by calling him "old man".