|Created by||Akira Jotaro (aka Justice0)|
|No. of episodes||24|
|Run time||23-24 minutes|
The story takes place in modern-day Tokyo and in an alternate world known as Flipside. The story is about a weak and cowardly boy who turns into the opposite version of himself to fight against monsters in Flipside called Alters.
As Shizuo Jakugano starts his first day of his new school year as a first-year student in high school, he meets with his childhood friend, Tenma Shurui, on the way to school and was bullied by her again like in their past, making them almost late for school. During his first day of school, he had already gotten the nickname, "Yowai-kun" (a pun on "弱" meaning "weak" which is also the first kanji of his family name just adding in the "い" kanji) because of his name and his weak body, and also because Tenma kept calling him "Yowai-kun" as making fun of him even though she actually prefers to calls him "Shi-chan". Not soon after the school day had ended, Shizuo suddenly dissapeared from the school yard when Tenma was still talking to him as they were walking home; his alter ego had appeared and he had actually jumped into Flipside, a world also known as the "Upsidedown Earth," the mirrored world of Earth where no one besides monsters known as Alters live and appear at random times to eat their real selves. As Shizuo's alter ego fights against the Alters, Tenma works up the nerve to confess to him her true feelings while not knowing anything about Flipside or Shizuo's second personality.
- A weak, cowardly, shy, and unlucky boy who is constantly picked on by his childhood friend, Tenma. His alter ego is almost the complete opposite of himself, since he is originally a weak and shy coward, his alter ego is a strong and outgoing fearless person. In Flipside, he has the ability to create certain weapons out of nothing; his weapons are a giant cannon gauntlet named Geist, a beam katana named Phantom, and a automatic handgun named Ghost. His name means "Weak but quiet" (弱が静雄 Jaku ga shizuo) which is also his normal personality. He is only talented in art, making the art club the only club he could join since none of the other clubs would take him due to his clumsiness. He is voiced by Kouki Miyata.
- Shizuo's childhood friend who likes to bully Shizuo but hates it when other people bully him. She secretly loves Shizuo but can never say it and blushes just when she thinks about it. Her name means "kind and heavenly" (種類と天馬 Shurui to tenma) which is ironic due to her physical behaviour but a perfect match for her inner personality which is shy but very kind and sincere. She is very athletic and is also the ace of the girls' track team. She is voiced by Asami Shimoda.
- The Alter monster of Tenma. She represents the inner frustrations of Tenma and her stress. Due to Tenma's frustrations, she was strong enough to evolve above the average Alter and become the mastermind of the school counselor's death, who was helping Tenma before she died. She is voiced Asami Shimoda.