Tomohiko Taniguchi, a special adviser to former Japanese Prime Minister Shinzo Abe, said Abe was "one of the most transformative leaders" of Japan.
"I think it's going to be an equivalent of JFK's assassination day. ... It's been a day of sadness, grief, disbelief, and for me, tremendous anger. People are finding it very much hard to digest the reality. I think it's very much an isolated event conducted by very much an isolated person. Nonetheless, that isolated incident killed one of the most transformative leaders of the Japanese history," he said.
He recalled Abe as a kind man and someone who wanted to usher Japan forward.
"He and Mrs. Abe did not have their own child, and he wanted to bring Japan to the younger generations as a country that is prosperous and future-oriented," he said.
"Once you are befriended with him, you get a lifelong friend," he added.
Taniguchi was an adviser to Abe from 2013-2014 and wrote foreign policy speeches for the former leader.
"I would very much like to see his legacy lasting, because there are very few options available for Japan. It's a maritime nation, and it's sitting on the periphery of a huge land mass which is being dominated by three nuclear power nations — Russia, North Korea, China — none of which is democratic. So Japan badly needs alliance partners like the United States, which Shinzo Abe tried very much hard to do," he added.