Board Thread:Speculation House/@comment-68.9.104.186-20150101031449/@comment-4010415-20150112023817

His weapon also turns into a trident. The only reason it turns into a naginata is because the blade of the naginata form makes the trident form actually practical in battle.

Either way, all of the characters have a character from a classic story that they allude to. Neptune alludes to Neptune/Poseidon, but his appearance is based on a Korean pop star.

Also, Neptune's emblem is a trident. It's on the tongues of his shoes.