First, you need to establish a good backstory for Issei. Understand his character traits, his relationships, and his goals. Then, come up with a strong reason for his betrayal. It could be something like a broken promise or a misunderstanding. Next, plan out how his betrayal will affect the other characters. Will they be shocked? Angry? Sad? Write their reactions realistically.
It could be his fellow team members. They might betray him out of greed for power. Maybe they thought that by getting rid of Issei, they could gain more resources or a higher position within their group.
Well, perhaps Issei was betrayed by his friends who he trusted deeply. This betrayal could be due to jealousy, like they were envious of his powers or popularity. As a result, he snapped and started to take revenge on them. He might use his unique abilities in unexpected and extreme ways.
A common plot element is the shock of betrayal. Issei is usually shown as a trusting character, so when he is betrayed, it's a huge emotional blow. Another element is his struggle to come to terms with it. He might question his own judgment and relationships. Also, often there is a part where he decides whether to seek revenge or forgiveness. For example, in some fanfictions, he initially wants revenge but then realizes that forgiveness might be a more noble path.
One common plot could be Issei being betrayed by his friends in the Occult Research Club. Maybe they believe false rumors about him being a traitor to their cause. For example, an enemy might plant evidence that makes it seem like Issei is secretly working for a rival faction. Another plot could involve Issei being betrayed by a love interest. She might be forced to turn against him due to some dark magic or family pressure.
One common plot twist could be that Issei betrays his friends for power. Maybe he's lured by a powerful devil who offers him unimaginable strength on the condition that he turns against his comrades. Another could be a misinformation scenario where Issei is tricked into believing his friends have betrayed him first, so he retaliates.
One popular 'betrayed Issei' fanfiction might be 'Issei's Betrayal and Redemption'. It delves into a storyline where Issei faces betrayal from his comrades and has to find his way back. Another could be 'The Betrayed Dragon', which focuses on how Issei copes with the emotional turmoil of being betrayed while still maintaining his inner strength. There are also many fan - made works on platforms like FanFiction.net that explore this theme.
Often, a power - hungry character might betray Issei. In the world of the fanfiction, power is crucial. So, someone who wants more power than Issei may see him as an obstacle. They could betray him by stealing his power - up opportunities or even directly stealing his power if there's some sort of magic or ability transfer in the story. Also, a character with a hidden agenda related to the overarching plot of the fanfiction world, like a secret organization trying to control the balance of power between devils, angels and fallen angels, could use Issei and then betray him when he has served their purpose.
At first, he's likely to be shocked. Issei is often portrayed as a character who trusts easily, so betrayal would come as a big surprise. He might not believe it at first and try to find reasons to justify the actions of the person who betrayed him.
I'm not entirely sure as the description is rather unclear. It could potentially be about a character named Issei in the 'DxD' universe and some sort of action related to a fanfiction about him. Maybe it's about exploring or creating a fan - made story where Issei is involved in a stroking action, though without more context it's hard to be specific.