ONE Flyweight World Champion Geje "Gravity" Eustaquio will be keeping a close eye when Demetrious "Mighty Mouse" Johnson makes his promotional debut at ONE: A New Era in Tokyo, Japan on 31 March. 

Johnson is set to lock horns Yuya “Little Piranha” Wakamatsu in the opening round of the much-awaited ONE Flyweight World Grand Prix tournament. 

Eustaquio attained his career-defining moment last June when he defeated Adriano “Mikinho” Moraes by razor-thin split decision in their rematch at ONE: Pinnacle of Power. 

Even though he comfortably sits on his throne as the lionized champion, Eustaquio does not mind putting his coveted crown on the line against a worthy contender, including Johnson who signed a multi-bout contract with ONE Championship this past October. 

The 29-year-old Baguio City native made no secret that he will watch the American's every move in his first bout under the ONE Championship banner in Japan. 

"I am excited to witness Demetrious Johnson's debut just like the rest of the world. He is without a doubt one of the greatest, if not the greatest athlete to set foot inside the cage," Eustaquio said. 

"The Flyweight Grand Prix will have the best martial artists in the world competing for a shot at my belt. It is my job as a champion to watch their every move and study how they do inside the cage.”

A total of eight world-class mixed martial artists will participate in the ONE Flyweight World Grand Prix. While the names of the other participants are yet to be announced, it is expected to include only the finest athletes that the organization has to offer. 

"The flyweight division is already stacked and talented as it is. The addition of Johnson takes this division to a whole new level," Eustaquio stated. 

The tournament will run for months, with the winner getting the ultimate prize of vying for the prestigious ONE Flyweight World Title. 

Eustaquio knows that a difficult task is up ahead, but the Filipino champion maintains that he is just as hungry as the rest of the competitors in the ONE Flyweight World Grand Prix. 

"Literally everybody in my division wants to become a champion and take this belt," he stressed. "I am just as hungry, if not more hungry to keep what's mine. I will do everything it takes to keep the belt in the Philippines.”