I'm trying to find this yaoi about two guys who are really good friends. One of them is looking for this jewel that's supposed to grant you wishes (I think) and the other guy is just following his friend because he loves him. In the end, we discover that the guy who loves his friend actually has the jewel and it's his heart. He gives it to his friend and dies in the process and the friend is full of regret. It might be a shounen ai.

I think this was a side story to Koori no Mamono no Monogatari .... or a side story to the author's other work, Silver Diamond.

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I reread Silver Diamond and there doesn't seem to have a side story or one shot with it...same with Koori no Mamono Monogatari. I checked the other works by the same mangaka: no luck.
Thanks for your attempt though!

Edit: I found it two years later; it's an extra from Demon Diary.

Last edited by Awesome Sauce at 1:42 am, Apr 12 2017