Build version 1.0 Japan world update scenery enhancement build notes:
Have so far fixed dark lines on river entrances for the whole south side of Japan from east to west..
-Fixed dark lines on river entrances.
-uncovered some hidden features will uncover more in future.
-added some cargo ships at various ports.
-added water to some rivers that were missing water more to do though.
-excluded water on most bridges in the tokyo bay area so far.
This is build 1 is far from finished and will be a huge ongoing update, please be patient as only myself working on it.
I don't see this add-on having any extra impact on performance of MSFS.

Build 1.5 notes:
-have fixed more dark lines at river entrances along the rest of the south coast of mainland Japan and up and around the west coast and started the north side.-added some cargo ships and couple of oil cargo ships.-Uncovered more hidden features under the water.-fixed more rivers with missing water.-fixed some areas along the coast with missing water.-fixed some terrain height issues.

Build 1.6: Made my way round the north west of mainland Japan:
-Fixed more dark lines at river entrances.
-added water to some rivers.
-removed water covering scenery.
-uncovered more hidden objects under the water.
-added more solar panels.
-added water along the coast to cover areas missing water.

Build 1.8:
-added around 30 missing windmills.-Fixed more black marking in river entrances.-uncovered more hidden features.-added a couple of appropriate ships.-fixed some water issue's along beaches.Almost completed the first pass around mainland japan.
To install this add-on download the zip file and unzip into the flight sims community folder easy as that.
If you install any 3rd party japan add-ons in future you may need to order my add-on below them in the content.xml folder. to do this follow this file path below: 
go to drive c > users > your username > app data > local > Packages > Microsoft.FlightSimulator_8wekyb3d8bbwe >
local cache > double left click the content.xml folder and open with notepad.
When in the content xml just make sure my Japan add-on is below any other japan content so their update doesn't overide my edits unless you intend to then it doesn't matter.
This is what you need to copy and paste below other Japan add-ons:
Build 2.0:
-Fixed the last of the river mouth dark patches.
-removed water covering features.
-added water to fix coastline edges.
-added some ships when appropriate.
-added some water to a couple of rivers where it was missing.
-completed first pass round mainland japan.

  

(DO NOT EDIT ANYTHING IN THIS FILE just copy and paste and make sure all lines line up)
I will add I think but not certain that the sim re-writes the content.xml folder at every start up.
(I AM NOT RESPONSIBLE HOWEVER UNLIKELY IT IS SHOULD YOU MESS ANYTHING UP IN THE content.xml folder.) 

Make sure to click follow when downloading so that you will be notified when a new update is released.
There is a donate button if anyone wants to reward me for my work, but will never be compulsory and no pressure to donate.