According to a statement on Isshi's official website, he was found dead in his home on July 18.
However, the statement made no mention of how he died; only saying that Isshi's funeral has already been held at an undisclosed location, as his family had requested.
In addition, the statement also said that Isshi's upcoming concerts on July 27 and July 27 will serve as memorial events to mark the his passing instead.
Kagrra was originally known as 'CROW', but the band was renamed 'Kagrra' after they signed with music label PS Company in 2000.
Over the years, Kagrra had built a reputation for wearing fanciful costumes inspired by traditional Japanese styles whenever they performed before announcing in November last year that the band has decided to split up.
Isshi embarked on a solo music career after Kagrra split up and was scheduled to release his new single in September 2011, but passed away before it could be released.