This is an original WWII manufactured Type 90 Japanese KIA bring-back helmet. The helmet exhibits an entry wound at the wearer's left side, with the exit at the right. The helmet's suspension system has been cut-out, most likely done by the Marine who dealt the damage. The front of the helmet exhibits a "ghosting" outline of a star badge, signifying use by the Japanese Army. The helmet's interior features the original owner's ID hand-painted in Kanji.
WWII KIA Imperial Japanese Army Type 90 Helmet