HxHEnthusiast
The first condition was a... can you even call that a condition, i like the hatsu and its probably one of the best uses of conjuration, so well done, but 400km/h really? aint that a bit too fast, ik meruem and netero are faster than sound but still its just the start of the fic and bro's already faster than killua when hes using speed of lightning.
You cannot be sure that at that scene he was running at full speed. Maybe he was conserving his energy since higher speed=higher nen consumption. So maybe he wasn’t going all out. About googling, some said the same as you while others said 50 mach while others said 100 m/s(3600km/h) so yeah
_Water_:killua doesnt actually move at the speed of lightning, thats just the name of the ability, he moves at around 360km/h, we can find this out by looking at after the chimera ant arc where he carries alluka while being chased by the granny tsubone, using math we can fgure out his speed and then times it by about 1.5 because he's also carrying alluka which is slowing him down, i dont really remember the original statistics of how it was figured out but if you search it up, im sure someone will tell you.