The talented pair have been impressive during Gamba's Asian Champions League campaign so far and Nishino believes they can be used much more as the season progresses.
Nishino gave 17-year old Usami a start in the J-League against Omiya Ardija a couple of weeks ago whilst 19-year old Otsuka was brought on for the second half and their showings in the domestic league were praised by the coach.
"I think they did well. Overall they did a good job. For Takashi, it was a situation where I wanted to change him, but I felt something strong and powerful from him in his first full match," Nishino said.
"Otsuka played very calmly. They are good additions to the team and it was a big achievement for them."
But now Nishino knows he has to continue throwing down the gauntlet to the pair so they keep thriving and developing as players.
"More and more, I have to make greater demands of them. I need to be stricter with them so they keep improving," he added.