It's not called “Lunar Legend Tsukhime” It's just called “Tsukhime”.

Second, it's not a “Porn Graphic Novel” it's a “Eroge Visual Novel”

Besides, the Eroge parts are minor and unimportant to the story.

Nanaya Shiki is an assassin who awaikens from Tohno Shiki’s blood cuz Shiki is originally a Nanaya and not a Tohno.

V Akihe comes from the demonic blood of Tohno Akiha.

Arcueid is a vampire and W Arcueid or Red Arcueid is a form of her where she sucumbed to her blood lust. ( So normally won’t consume blood ).

Sion is also a vampire but not compleatly yet however the vampire blood is taking over her -> V Sion.

Mech Hisui is made by Kohaku.

Thise split personalities are separate characters cuz the boss of the story, Warachia has the power to give form to fears…or to be exact he is fear himself. ( He is not a living creature but a phenomenon ) As fear taking shape he materialises the bad side of all characters since they fear those sides.

W Len is made by Aoko from the remnants of Warachia after he was killed in the original Melty Blood and cuz of that W Len has simular powers.

Oh and btw. The original game ( What you simply stated as porn…-_- ) is not about porn at all thou it has some. How ever as a Type-Moon fan ( Type-Moon created Tsukihime, Fate/Stay Night and Kara no Kyoukai ) I can say the story or should I say the characters over shadow the porn sceans and make them basically unecesery cuz those who play tsukihime dose it for the story.