In Highschool DxD fanfiction, a common trope regarding Issei is his growth as a character. He often starts as a pervy and weak character but gradually becomes stronger and more noble. Another aspect is his relationships, like his complex interactions with the various female characters in the series.
I haven't actually read a specific fanfiction about Issei's 'cock hurt' (assuming this is a rather strange and perhaps inappropriate scenario). However, in general, fanfictions in the Highschool DxD universe often explore different aspects of the characters. If there is such a story, it might be a very unique and out - of - the - ordinary take on Issei's character, but it also might not be in line with the more positive and common themes in the official series.
One great Highschool DxD Issei magic fanfiction is 'Issei's Magic Evolution'. It shows Issei developing unique magical abilities that are different from his usual power set in the original series. This adds an interesting twist to his character.
One idea for a fanfiction about Issei's birthday could be that the Occult Research Club throws him a surprise party. They decorate the clubroom with all his favorite things, like pictures of his favorite heroes and a big banner that says 'Happy Birthday Issei'. Rias could present him with a special gift, perhaps a new piece of sacred gear that has been customized just for him.
One common theme is power escalation. Since Issei is OP in these fanfictions, the story often focuses on how he continues to gain and control his ever - increasing power. Another theme is harem - related, as in the original Highschool DxD, Issei has a harem. In the fanfictions, his OP status might attract even more characters to his harem, and the dynamics within the harem change because of his new power level.
Another reason is the fan community. Highschool DxD has a large and passionate fan base. When a fanfiction focuses on Issei and magic, it combines two elements that many fans are interested in. Fans like to share and discuss these fanfictions, which further spreads their popularity. Also, it allows fans to explore their own ideas and interpretations of the characters and the world, which is always appealing.
He could receive a mysterious letter inviting him to a secret location on his birthday. When he arrives, he finds all the mythical creatures he has befriended over the time. They have prepared a grand feast for him with all kinds of magical foods and drinks. And there's a special performance by some of the most talented supernatural beings, like a dragon doing a fire - breathing show just for his entertainment.
Character development is a crucial element. A good highschool dxd fem issei fanfiction will show how Issei's character changes due to her new gender. She might have different insecurities or strengths. Her relationships with other characters like Akeno or Koneko will also develop in new ways. Additionally, the plot often revolves around her trying to find her place in the world, whether it's among the devils, the angels, or the fallen angels. This journey of self - discovery is a common and engaging theme in such fanfictions.
In some fanfictions, Issei might develop a more serious personality earlier on. Instead of his usual comical and pervy self from the start, he could be shown as someone with a greater sense of purpose, perhaps due to a different backstory or a unique encounter. For example, if he had a more tragic event in his past related to the supernatural, it could shape him into a more brooding and focused character.