The Return of the Corpse King

A brief description of the manga The Return of the Corpse King:
“How can my past self get so excited doing all those embarrassing things!?”
When he was in the third year of middle school, Hizaki Shiou was summoned to another world to save it. After defeating the Demon King, he was forcibly returned back to the present day. Yet another three years later, he is summoned to the other world once again, this time to stop the rampage of the secret society “Helheim.”
That organization was supposedly actually the one that he had founded during his chuunibyou phase, where he called himself the “Corpse King”—a dark past too embarrassing to remember!
Someone seems to be impersonating the name of “Helheim” and tarnishing its reputation. To uncover the truth behind this mystery and clear the organization’s name, the Corpse King reunites with his former subordinates, the “Hakkai,” who once made Helheim the strongest it had ever been. While agonizing over his dark past, he begins to take action in the other world once again.
Their first stop is the Steel City of Gagiul—rescue the city struggling through famine as well as the pale-looking count’s daughter in distress.
“Helheim, moving out.”