Aomori-born Okada, who participated in the match against fellow-debutant Masafumi Kamiyama, was stopped in the early stages of the fourth round and rushed to hospital after collapsing.
The 21 year-old underwent an emergency operation after doctors diagnosed the youngster with an acute subdural haematoma, although Okada never pulled through despite fighting for his life for over two weeks.
Okada is the latest fatality to rock the sport on the back of some higher-profile injuries, which have included the now rehabilitating heavyweight Magomed Abdusalamov, who almost died following a brutal fight with Mike Perez in November.
And the tragic Frankie Leal, who passed away at just 26 following a bout in his home country of Mexico last October.
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