Phosphophyllite

Phosphophyllite, simply known as Phos, is the main protagonist in Land of the Lustrous manga and anime series, and the youngest gem to begin with. They were presented as a weak and jovial person from the beginning, but as the story goes, Phos started to change in both body and mind, and eventually started to do questionable motions after their head was replaced with the head of Lapis Lazuli.

Under Lapis' influence, Phos started to betray Adamant-Sensei, who was revealed to be a machine made for Lunarians to pray and made them into afterlife. They started a rebellion and made several other gems to leave for the Moon, in order to force Adamant-Sensei to go onto his duty, even at the price of departing several working partners.

As a result of their actions, Phos is considered as one of the main antagonists of Moon Arc (on Adament-Sensei and other Gems' side) alongside Prince Aechmea and Carnigorn.

They're voiced by Tomoy Kurosawa.

Personality
At the start of the series, Phos is one of the weakest Gems in the whole series, with 3.5 of hardness and the weakest flexibility out of all gems. They're also the youngest gem appeared in the first part of series. They started as a jovial, casual and arrogant person who talked big and had a flexible way of thinking. However, Phos was interior fragile, being afraid of getting useless and was often hestitated in a fight with Lunarians. They also cared for Cinnarbar greatly as they find Cinnarbar's solitude sad.

Nonetheless, after witnessing Antarcticite's abduction at the hands of Lunarians, Phos started to change in their personality and turned calmer, less hestitated in a fight. Traumatized by the events in winter, Phos started to turn more powerful, more modest and more ruthless, and in times more melancholy and solemn, no longer being energetic and bubbly. They also grown more and more disturstful to Sensei after the incident with Shiro, discovering that he could communicate with Lunarians.

After being attached with the head of Lapis Lazuli, Phos became much more intellegent due to merging with the mind of Lapis. They became more level-headed, cautious, observant and above all - manipulative, just as Lapis had been. They now focus more on their own goals and the safety of the others Gems over their concern for Adament-sensei.