I Really Didn't Mean to Become Ultraman

As an investigator sent out by Earth to collect information about ascension, Xia Chuan only has to live in a new world for the required number of years, then die a normal death, to complete his mission and return to Earth to enjoy a happy life. However, after finally making it through the required time and finding a chance to step in and save someone, he opened his eyes to find not the ceiling of his old home, but a towering red giant as flamboyant as a lion.

"Earthling, open your eyes! Your spirit of saving others without regard for your own safety moved me. Now, I shall share my life with you!" said the passing Showa-era King of Combat.

Fortunately, this world had enough crises. Titanic beasts underground were awakening, prehistoric monsters were stirring from their slumber, and the scheming Mefilas were secretly unleashing Kaiju... Xia Chuan believed that as long as he was reckless enough, he could surely die his way back home.

But...

"Good! Just like that! Let your hot-blooded spirit burn!" The great lion transformed into Gen Ohtori, wearing the same smile as Dan Moroboshi. "Come on, don't run away. Charge at the jeep!"

"Stay away from me!"