where to ask girlfriend to marry me

I'm planning on taking my girlfriend to japan in a year or so and i plan on asking her to marry me at a Japanese garden during the cherry blossom festival and i'm wondering where would be the best and less crowded to ask

The Imperial Palace itself has plenty of cherry blossom trees and has powerful feng shui powers (so they say) which just makes you feel good all over - increasing the chance she'll say yes! -- j/k =)
But, if you're looking for as close to isolation as possible, you won't have luck in a public place like the Palace.

Idea#1
Reserve a Japanese Tea Ceremony house which is VERY quiet, has GREAT scenery (its part of the whole ritual) and has cultural meaning as it's something the samurai elites did back in feudal times as both a political and romantic practice (now its a high-class hobby).
I'd avoid arranging your engagement ring, etc to be put into the tea during the mixing process (another part of the ritual),hoping to get a nice surprise from your gf because the resident tea master probably won't want to ruin his expensive tea with foreign objects. Instead, I suggest this. There is normally a sweet cake/treat served after you drink your tea and this is where you can arrange for the ring (beforehand)to appear.
Idea#2
Then again, if you don't plan to do the "plant the ring" trick, then the tea ceremony itself should be a more than satisfactory ploy to calm the soul for proposing.
Idea#3
Indoors proposal - The Grand Ark Hanzomon Hotel, located on the Hanzomon-side of the Imperial Palace, has an upstairs lounge with a stunning view of the cherry blossoms. Plus it's quiet with no crowds at all and if you phone the hotel a week beforehand asking to have the place to yourselves for an hour, it should be arrangeable. (if you need help, drop me an email thru japan-guide). Not 100% private but its comfortable and you never know about the weather (this year we only had a few days of sakura, the rest got blown away by irregular gusts and rain)