Perhaps the 'sex quirk' is really a 'bond - enhancing quirk'. Izuku can strengthen the bonds between people, whether they are friends, family, or comrades. He does this by emitting a kind of positive energy. In a battle scenario, this strengthened bond can lead to better teamwork as the heroes feel more in sync with each other. In a non - battle situation, it can help heal rifts between characters and create a more harmonious environment.
The quirk could be turned into a 'vitality quirk'. Izuku's quirk might be that he can sense and transfer a type of life - force energy. This energy is related to the concept of sexual energy in a very abstract way in that it represents the life and passion within a person. But in the context of the story for a younger audience, it's just about him being able to boost the energy of his friends when they're tired or weak, or using it to heal minor injuries.
Some characters might be immediately terrified. They could avoid Izuku or even try to drive him away. For example, classmates who don't understand his quirk might spread rumors about him.
In 'The Healer of UA', Izuku's healing quirk is more complex. It requires him to concentrate and visualize the injury being healed. He can also transfer some of his own stamina to the injured to speed up the process. This makes his quirk not only about physical healing but also about his own sacrifice and determination.
Izuku could develop by learning to accept his vampire quirk. At first, he might be scared or ashamed of it, but as he realizes the potential it has for good, he grows more confident. For example, when he saves someone using his vampire - enhanced abilities.
In a fanfiction, the development of Izuku having a black fire quirk can be really multi - faceted. First, the visual aspect of the quirk can be described in detail. The black fire could have a smoky, otherworldly look that sets it apart from normal fire. Emotionally, Izuku could struggle with the fact that his quirk is so different from what he expected. He might feel like an outcast among his peers. Then, there could be a story arc where he discovers a hidden power within the black fire quirk. For instance, he might find out that it can absorb other forms of energy. This would not only make his quirk more powerful but also open up new storylines about him learning to use this new aspect and facing new enemies who are interested in his unique ability.
In some fanfictions, Izuku might discover he has his father's quirk during a moment of extreme stress. For example, when facing a powerful villain that he couldn't defeat with his own quirk, suddenly a new power, which turns out to be his father's quirk, emerges.
His relationships with his friends would likely become more complex. If he starts using his time quirk to change things, his friends might not remember the original timeline, but Izuku would. This could create a sense of isolation for him as he holds memories that no one else does.
One great 'Fem Izuku has a Quirk' fanfiction is 'Powerful Ascent'. In this story, Izuku's quirk is a unique combination of telekinesis and energy manipulation. The author does an amazing job of exploring how a female Izuku would face the challenges in the hero academy with such a powerful quirk. It also delves into her relationships with other characters like Bakugo and Todoroki in a really interesting way.
The Gamer Quirk also changes Izuku's relationship with others. He can now offer unique insights based on his quirk. For instance, he might be able to analyze a villain's attack pattern like it was a boss fight in a game. His friends and allies can then use this information to their advantage. This makes him a valuable member of any team. At the same time, it also means that he might be seen as a bit of an oddball because his thinking is so different from the norm. But overall, it helps him form deeper connections with those who understand and appreciate his quirk.
I'm sorry, but I don't have specific fanfiction to recommend directly. You can try searching on popular fanfiction websites like Archive of Our Own (AO3) or FanFiction.net. Just type in 'izuku sex change quirk' in their search bars, and you'll likely find relevant works.
One common theme could be self - discovery. With the sex change quirk, Izuku might have to re - evaluate his identity. Another theme could be acceptance, both from himself and from those around him. For example, his friends and family might need to come to terms with the change.