In a Mermaid Quirk fanfiction, Izuku's relationship with his teachers would be different. Aizawa might be more cautious about sending Izuku on certain missions because of his mermaid - related needs. And All Might could play a big role in helping Izuku understand and control his new quirk, which would deepen their mentor - mentee relationship.
His relationship with Bakugo might change. Bakugo could be jealous of Izuku's unique quirk at first. But later, they might have to team up for an underwater mission. Izuku's friends from school could also be in awe of his mermaid quirk and might want to learn more about it.
He might become more confident. Having a powerful dragon quirk could make Izuku realize his own strength, and he'd carry himself with more assurance. For example, he wouldn't be as shy when speaking up in class or to other heroes.
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.
His personality could be split. On one hand, he would still have his core values of heroism and kindness. But on the other hand, the dark quirk could bring out a more ruthless side. He might find himself having internal debates between using his power in a traditional heroic way or succumbing to the darker impulses that the quirk brings. This internal struggle would be a major part of his new personality in the fanfiction.
His relationship with Bakugo might change. Bakugo, who used to look down on Izuku, might now be a bit jealous or even more competitive as Izuku's Dragon Slayer quirk is very powerful. With his friends like Uraraka, she could be in awe of his new quirk and support him more actively in battles. Izuku might also attract the attention of some of the more powerful heroes in training, who want to team up with him because of his unique ability.
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.
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 relationship with All Might would also be affected. All Might might be more cautious about Izuku's quirk as it's very powerful and could potentially disrupt the fabric of time. Izuku, on the other hand, could use his quirk to go back and learn more about All Might's past, which could strengthen their bond as he gains a deeper understanding of his mentor. However, it could also create a rift if Izuku discovers something in the past that he doesn't like about All Might's actions.
His relationship with his teachers could also change. The teachers might be more interested in studying his sentient quirk, which could lead to special training or extra attention. This could either make Izuku feel special or pressured, depending on how the author writes it.
In fanfiction, Izuku's pride quirk could make his relationships more complex. If his quirk is related to personal pride, he might be more self - focused at times, which could cause some friction with his friends. For example, he might be so determined to prove his pride in his quirk that he doesn't listen to their advice.
His relationship with Bakugo would likely change significantly. Bakugo might initially be jealous of Izuku's unique shadow quirk. But over time, they could develop a more competitive but respectful relationship, as Izuku's shadow quirk gives him new ways to fight. With his friends like Uraraka, Izuku's new quirk could make him seem a bit more mysterious. Uraraka might be curious about how his quirk works and they could bond over her trying to understand it.