Gloxinia is one of the members of the Ten Commandments. He was one of the more interesting villains.
Him and Drole hold a fancy fighting festival to bait Meliodas into a trap.
And get the crap beaten out of them for it.
After losing to Meliodas, they decide to mentor King and Diane. As they are not demons, but a fairy and a giant. They give them the chance to relive their past to see if they made better choices.
Gloxinia made the wrong mistake by giving into madness and murder when his sister and friends were brutally attacked by humans who hated Stigma. I understand, but I don’t know why that led him exactly into the Ten Commandments.
His fighting moves were pretty impressive, like a much better version of King’s powers. Since he was the original Fairy King, it makes sense.
He dies against Chandler when the demon tried to attack and murder several members of the Seven Deadly Sins. Giving him a path to redeem himself for his alliance with the demon race. A very sad demise.