It might also change his relationships with other characters. His friends could be both amazed and a bit envious. And his enemies would start to see him as an even greater threat. For example, Bakugo might feel more pressured to compete with Izuku who now has an additional powerful quirk.
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.
One implication could be a change in his relationships. His friends might be initially afraid or distrustful. For example, Bakugo could see this as a sign of Izuku being a real threat now, instead of just a rival. Also, the teachers at UA might have to deal with a whole new set of problems regarding Izuku's training and control of his dark quirk.
A sentient quirk for Izuku in fanfiction could have a huge impact on the plot. It could be a source of both power and trouble. For instance, villains might try to target the quirk specifically, seeing it as a valuable asset or a threat. Izuku would have to constantly protect it while also using it to his advantage. The quirk could also communicate with other sentient entities in the fanfiction world, opening up new storylines and alliances.
His relationship with his mother could become more complex. She might be worried about his new nature and try to protect him more. With his friends, like Bakugo, they might initially be scared or distrustful when they find out about his quirk.
In fanfiction, Izuku often has unique ways to cultivate his quirk. One common scenario is that he focuses on intense physical training. Since his body was initially not as strong as it could be to handle his powerful quirk, he might do a lot of strength - building exercises like weightlifting and running. This not only helps him control his quirk better but also increases his overall combat capabilities.
He could have the power of flight. Just like a dragon, being able to soar through the sky would be an amazing ability. He might also have enhanced strength, as dragons are often depicted as very strong creatures in mythology.
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.
His relationships with others might change. His friends could view him in a new light, either with admiration or envy. Enemies might start to target him more, seeing him as a greater threat now that his quirk is unlocked.
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.
In many fanfictions, Izuku might unlock his quirk through intense emotional experiences. For example, a moment of extreme anger or determination could trigger it. Maybe seeing his friends in great danger and feeling a strong need to protect them could be the catalyst.