‘Henshin’ is a Japanese word meaning ‘transformation’. It is a common theme in anime and manga for a character to transform into a stronger version of themselves. Yugi Muto from Yu-Gi-Oh! and Eren Yeager from Attack on Titan both have a henshin, and they both acquire it in similar ways.
Yugi Muto received the Millennium Puzzle from his grandfather when he was about eight years old. (Eight years before his sophomore year.) For years, the solution to the puzzle evaded him, until one day when he protected a guy named Jonouchi from getting physically assaulted. Jonouchi would pick on Yugi mercilessly and constantly tease him for being a ‘sissy.’ Yugi’s kindhearted nature would not allow him to see Jonouchi get assaulted, despite the fact that Jonouchi would pick on him. Yugi stopped the bully Ushio from further assaulting Jonouchi. Jonouchi realized that Yugi’s strength doesn’t come from being physically strong, it comes from standing up for what’s right, even if all the odds are against him. Because of Yugi’s act of kindness, Jonouchi decided to return the piece of the Millennium Puzzle that he stole. With the final piece of the Millennium Puzzle, Yugi was able to solve the puzzle and bond with the soul of an ancient Pharaoh, who was also and invincible game-player. Yugi’s henshin allowed him to unleash justice upon the bully Ushio for injuring him and Jonouchi. Because of Yugi’s ‘courage of kindness,’ he was able to become best friends with Jonouchi.
When Eren Yeager was ten years old, his father injected him with a serum that gave him the ability to transform into a titan. Eren was not aware of this power, however, until he saved his best friend Armin from getting eaten by a titan. In doing so, Eren himself got devoured. While inside the belly of the beast, Eren witnessed others who had shared the same fate as his. He saw people whose lives and dreams were cut short due to the horrors that surrounded them. Enraged by the sight he saw, Eren finally transformed for the first time and escaped the titan he was inside. With his newfound transformation, Eren now had the ability to fight hand-to-hand with the titans. His comrades believed they could use Eren’s henshin to win their freedom.
Eren Yeager and Yugi Muto both received their power to transform from a father, or a father-figure, and first activated their henshin after saving their best friend.