Firstly, what video games could possible constitute mori? In a world of magical girls and super villains, the pickings appear pretty slim. Luckily, I've unearthed a few titles that may suit a mori mindset. I chose to include only Nintendo DS games (for now?) because I am most familiar with them. They portability and customization options also make them ideal for the mori enthusiast.
On to the games:
Rune Factory: This JRPG has beautiful, almost watercolor-quality, whimsical graphics. From what I have seen, this game allows you to tend to a garden, interact with animals and much more complete with a story line.
Harvest Moon DS Cute: This game allows you to live as a farmer, growing and selling a variety of crops, tending to animals and even entering them in fairs! This cute game has a bit of level grinding, but is still plenty enjoyable to play.
Time for the accessories! Accessorizing your DS through cases, skins and straps can be very useful in creating your desired natural kei-aesthetic.
Here is a forest green silicon case for your Nintendo DSi avaliable on Amazon
This is a cute card/cartridge holder from Paper Plane Products
Here are a few cute DS cases also from Paper Plane Products
And yet another item from Paper Plane Products; a cute coffee-themed DS skin
I hope these ideas will help you spruce up your DS!