Yeah, below is the picture, there are still some very stubborn grass pieces glued to the surface. I tried the below :
-Meguiar NXT shampoo + wash mitt
-Turtlewax bug & tar removal (I think this does nothing)
-Osren medium strength APC foam with brush
-IPA spray & wipe
-zippo lighter fluid & wipe
-OEM claybar + clay lube (does remove some grass, but not all)
-mother's cleaner wax + sponge (also removes some)
-meguairs ult polish + sponge
-finger nail scrapping (on stubborn pieces, still very hard to remove)

I starting to think maybe need to sand them & slowly grind them away or something, but dont have the skills to do this.

Thanks for the advice guys. The thing I noticed with this 1 week dried grass is that the pieces can be removed are already removed, but there still there are some tiny prices that is still there. Even scraping with finger nails is not easy to scrape them off.

Quite stressed out about this so I decided to just leave it as it is and not drive myself nuts. Maybe future washing will eventually scrape them off bit by bit or something. Luckily the remaining grass pieces are barely noticeable on dark paint. Just worried they may affect durability of wax / sealant due to bonding on unclean paint.

Just to add :
-tried WD40 & wipe, doesn't work.
-not yet tried vinegar & onr, too tired to continue, will try in future.
-not quite sure what sticker remover Bro therain01 mentioned? Zippo lighter fluid?

Got my new car and surprisingly the original factory paint has imperfection such as dust nibs (dirt stuck onto the paint) on the hood/roof which is the size of sand and noticeable only at certain angle. I am surprised since it's a Japanese car and I believe car paint factories need to be dust free, hence such occurrence will be very low. Anyone has encounter such imperfection and what do you do with it? Just leave it or remove it? Personally I plan to leave it because removing it simply means cutting of a layer of paint but it's interesting to hear your experiences.