That Time I Got Reincanated as a False Dragon?!

Satorou Mikami was a normal guy with a mundane life until all of it changed at once.

<It hurts. There's so much blood>

[Confirmed: Pain nullification aquired. Building a body that does not require blood.]

<What a terrible way to go. How old am I and still a virgin. If it's true that turning 30 and still being a virgin gives you wizard magic, then I must be a great sage>

[Confirmed: aquiring the unique skill {Great Sage}... successful]

<I never got to finish that novel about the dragon that stole the world tree. If I were that dragon, I'd steal all the ladies.>

[Confirmed: Unique skill {Plunderer} aquired]

<Being a dragon would be so cool. What a shame the character was too much of a pacifist. I never got to the part where he actually turned into a dragon. He should have been so much more aggressive, like that demon he fought.>

[Confirmed: The individual's constitution will be rebuilt according to their desires. Aquiring True Dragon form... unable to aquire a True Dragon form. Attempting Sub-dragon constitution... failed. Attempting Dragon form... successful. Aquiring Spiritual form... successful. Applying demonic constitution... successful]

<If I was born earlier, would that have made a difference in my life?>

[Confirmed: Attempting to locate earliest possible point for incarnation... No compatable point has been found in the cardinal world. Searching for alternatives... Successful. Individual will incarnate into the underworld.]

<What is happening to me?>

[Notice: Individual has aquired a new species form as a false dragon.]

<What is that voice?>

[Notice: This is an effect caused be the Voice Of The World.]

<Shut up... can't a guy die in peace?>

Upon waking, Satorou found himself in an unfamiliar place... and he wasn't human anymore?
He got stabbed and now he's in another world? And what does demon constitution mean? False dragon? What does that even mean?