Complex sentence: Although Nobuhiro Watsuki had checked the script from the OVA, he gave it disapproval due to its sad ending, and he stated that it is not canon and should not be treated as canonical.
Split into simpler sentences: Although Nobuhiro Watsuki had checked the script from the OVA, he gave it disapproval due to its sad ending. He stated that it is not canon and should not be treated as canonical.