Wow, I love the poem. You judge prose in the English language on a completely different scale from poetry in the English language. Judged as poetry written in the English language, I'd call this pretty close to natural. Not perfect, but close. It's very powerful, in any case.
If this were my poem, I'd write it like this:
You waited for a lemon for such a long time.
Lying on that white and sad deathbed.
You took a lemon from my hand,
And bit into it with your beautiful teeth.
And a topaz-colored fragrance filled the air.
Those few drops of lemon juice I gave you
Brought you right back to me.
Your clear blue eyes smiled, faintly.
I felt life in the power with which you grasped my hand.
There was a storm in your throat.
You were on the brink of life.
Chieko was once again Chieko.
You put a whole lifetime of love into this moment and,
In this moment,
You took a deep breath like you were standing on a mountaintop.
And the engine stopped forever.
Under the cherry blossoms offered to your photo,
I put a fresh, shining lemon today as well.