One of his friends could be the cause, accidentally. Maybe a friend makes a deal with a shady character without realizing the consequences. This deal ends up putting everyone in danger, and Yami gets mad at his friend's naivete and the mess they've created.
Yami remains alive in the manga. The author chose to keep Yami as an ongoing character to drive the story forward and interact with other characters in various scenarios.
As far as I know, Yami doesn't die in the manga. The story might have twists and turns, but that particular event hasn't happened yet. Maybe there are rumors or speculations, but based on the official storyline, no.
One plot idea could be Yami going on a solo mission to a mysterious and dangerous land. He has to face powerful new enemies and discover secrets about his own past. Another could be Yami training a young and inexperienced magic knight, sharing his unique combat and magic knowledge.
To write a believable characterisation of Yami, focus on his rough exterior but also his loyalty to his squad. Show his love for food, especially Japanese food. Also, don't forget his unique magic style and how he uses it in combat.
A possessive Yami can create a sense of mystery in the fanfiction. Readers might wonder why he is so possessive. Is it love? Loyalty? Or something else? This can keep them engaged and eager to find out more about his motives.
In 'yami and tea kiss fanfiction', the writer likely has a creative take on their characters. This could involve changing their personalities slightly to fit the scenario. For example, Yami might be more vulnerable in this fictional piece, and Tea could be more assertive in initiating the kiss. The fanfiction may also play with different settings, like a romantic evening by a lake or a secret encounter in a castle.