That appears to be the Japanese title for the manga and anime series better known internationally as "ReLIFE".
Chapter 2: “Wait, my legs are short”
He wakes up in 2004. His mom’s cooking smells the same. His bullies are still terrifying—but now he notices their home lives are broken too. Instead of revenge, he uses adult negotiation to befriend the quiet kid who becomes a famous artist.
The story follows a protagonist who, after living a mediocre or perhaps regret-filled adult life, suddenly finds themselves transported back into their younger body. Unlike typical "Isekai" stories where the hero goes to a magical fantasy land, this is a "Regressor" story grounded in the real world—specifically, the late 20th or early 21st century.
After wishing for a second chance, he suddenly travels back in time to his childhood body while retaining his adult memories and personality. Now a "kid" again, he uses his adult experience and newfound confidence to confront the girls who once mistreated him and pursue the relationships he missed out on the first time. Key Characters
It represents the visceral frustration of modern adulthood. Search engines see %21 as just a character, but to fans, it symbolizes the urgency behind the desire. It is the sound of someone slamming their desk at 2 AM, staring at their unpaid bills, and whispering, "If I could just go back to being a gaki..."
: The narrative balances whimsical nostalgia with more serious emotional stakes. It often highlights the weight of the protagonist's decisions as they realize that attempting to correct the past involves complex consequences and personal growth. Narrative Focus