Max Flexer (Macho San in Japan) is the hyperactive fitness Demon Beast who appears in the episode Fitness Fiend. He was ordered to do a fitness workout with King Dedede and Kirby after they overate a very tasty snack. His methods are both extremely dangerous and unorthodox. He uses a bunch of strange machines to whip his clients into shape while shouting and rhyming. During his exercises, his clients also have to fight to survive while exercising. Max Flexer's methods worked however, and he crushes Kirby's belly causing him to upchuck the snacks and return to normal. Kirby then inhaled Max Flexer's headset and became Mike Kirby. Kirby sang a terrible tune like he did in previous episodes. In the midst of all the singing, Max Flexer covers his ears but was still overwhelmed by the terrible singing. He finally couldn't take it anymore and is destroyed in a huge explosion that caused the castle to crumble.
Max Flexer appears dressed as a traditional fitness instructor. Being a fitness instructor, he is also in great shape. He has curly pink hair, red wristbands, white shoes, and wears a retro-styled yellow jumpsuit with a red stripe running down it. He also wears a headset on the right side of his face and has brownish, tanned skin. He has stereotypical trainer's sunglasses that almost always have a shine on them. His mouth is very large, even larger than Kirby's, and is full of pearly white teeth.
Max Flexer is the only demon beast that has a last name.
Mike Kirby's singing is bad enough to actually crack Max Flexer's sunglasses.
Max Flexer appears in Kirby Mass Attack in the Kirby Quest sub-game, in Stage 17 of Chapter 2.
In the English version of Kirby Mass Attack, the music that plays often uses the word "hai" in it, which was the the main word that Max Flexer used in his song in the Japanese version of the anime. "Hai" is Japanese for "yes" or "yeah."
Treadmills are a lot of fun. You'll be fitter when we're done! Better keep on moving fast, or this race will be your last!
Japanese: Unless you run, you'll be split in two. You'll join the other world if you don't run ahead. You'd better keep running if you want to live. Punishment heaven, Go go heaven!”