I, the Invincible One, Became the Quintessential Quintuplets' Brother

A guy who thought he had worked out a successful future resolutely decided to start his life over.

But the world would soon show him through its actions: "A guy who's been asleep for fifty years shouldn't try to act young."

"..."

"Bro, I was wrong! Let's talk this out. Put away the orbital cannon first..."

Note: This is the second part of I Lost My Memory and Became the Quintuplets' Older Brother. The characters haven't changed much, but the plot has turned upside down.