Help Me Identify My Bike Serial No. : HZ100202418
tl;dr its a modern bike inspired by workman bikes of the 1950s.



Mayam is/was a bicycle company in Nagoya Japan, and was related to "Nittei Industry Co"  They were known for their "heavy duty carrier bicycles" which is where the double top-tube comes from.

 1970s advert.


Older advert reproduced in a calendar.

 Japanese "Guarantee Medal"  associating the names Mayam and Nittei

More info  http://chikutakurinrin.cocolog-nifty.com/blog/2011/08/index.html 



Your bike appears to be a modern reproduction "inspired-by" the older models.  Reasons:


The fork has nowhere near as much rake as the old bikes.  
Dual pivot front rim brake
No rear brake - loaded bikes take some stopping, though a coaster brake might work.
No carrier, nor lugs to fit a carrier
No mudguard mounts either.  A workman's bike gets used in the rain and wet.
Super short head tube.  Back then head tubes were longer - short ones increased stresses on the head tube/top/downtube weld areas.  Also related to load carrying limits
Deeper section wheels - these bikes would have had steel box section rims for strength while carrying loads.


Other - Not sure whats up with that bottle cage - might be some special modern thing that interfaces with a special bottle.