>>22873419I'll try to go through each fundamental part.
Flow, the choppiest bars and the smoothest bars in Japanese rap have very little difference. There is very little variation in the flow at all, it's almost always the exact same rhythm.
Syncopation, this isn't actually a commonly spoken about thing but this is how the rhyming and flow clash with the instrumental. Like being so off beat that syllables stand out more, or being so on the beat that you really have to focus on the words being said.
Just like flow, there is almost no variety in japanese rap, it's done in a similar way every time.
Poetry. Different cultures have completely different styles when it comes to the creation of poems. With English rap, in combination with the musical measure it allows for verse size that are remiscient of a regular stanza.
I don't know if there are rappers doing Haikus or whatever in their songs but even if they do, it won't sound as good.