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It would be easier and faster to say m rather than kk

M means million. Million means 6 zeros
1000000

Ok but you get my point. So why kilo* kilo and not mega?

Duelers are commonly known to say 1kk etc, if we were to say 1m infront of others it would look stupid probably we will say 1mil or 1milli but that's why we like the abbreviation of 1kk and we also say it cause it's short and simple

Just a norm since many people do it, nothing supernatural.

Most of the community subs 1000 as 1k or 10000 as 10k

So, 1kk as 1 million is just more easier on the mind.

It's all to do with most used unit of currency.

You have standard units for most things and for 99% of toribash transactions this is in thousand incriments. So it's much easier to relate everything to one form of measurement. In this sense 500tc becomes 0.5k and 1000000tc becomes 1kk.