I am searching for a manga/manhwa that I read 10 years ago.
I don't know if it was manga or manhwa because it was in Hong Kong and translated into Chinese. It was in one of those weekly "Jump" magazine.
From the first few chapters
On the way to school, the main character wanted to buy a birthday gift for his neighbor girl. He was drawn/called to a jewelry store, where he found a large bracelet with one huge diamond and one black stone. He didn't have enough money so the store owner sold him just the diamond part of the bracelet. After he left, black shadows came out of the black stone, killed the store owner, and burned down the store.
At school, one of the schoolmates of the main character wanted to see the bracelet and put it on the main character's arm, and the bracelet fused onto his arm. He got another gift for the girl (a dolphin ring) and she happily accepted it. The adopted brother of girl is the typical good looks, good grades, idol of all the girls type of character. He was super jealous that the girl chose the dolphin ring over the diamond ring he gave her. He was also drawn/called to the same jewelry store, now burnt to ashes.
The black stone threw itself into his eye and fused with it.
The diamond has the power of light and is able to give out light and heat. The black stone has the power of shadow and dissolves anything the shadow touches.
Example: The jealous brother cast a shadow on the support beam of a construction crane, ate away the support and dropped the crane onto the main character. The main character touched the falling crane and melted it like candy.
Later in the story
There is a jade necklace that can communicate with plants. A moon stone that gives werewolf like ability. A ruby that manipulates gravity. A blue stone that heals and more.