Maybe a 'Shadow Manipulation' quirk. It would fit his dark and stealthy nature. He could use shadows to hide, move around undetected, and even attack his enemies from unexpected angles. It would be like an extension of his ability to disappear into the night in Gotham.
He could have a quirk like 'Enhanced Intellect', which would further boost his already incredible detective skills. This would make him able to analyze situations even faster and come up with strategies on the fly.
Batman doesn't have powers like the characters in MHA, but his skills would still be extremely valuable. He could be seen as a sort of 'Quirkless' hero, much like Izuku was initially. His physical conditioning, martial arts mastery, and detective skills would set him apart. He might be able to outwit many of the villains using his intelligence.
Batman in the My Hero Academia world would likely be a bit of an outsider at first. His dark and brooding nature might contrast with the more colorful and often optimistic characters in MHA. However, his intelligence would be highly respected. He could use his detective skills to help solve some of the mysteries that pop up in the MHA world, like the origin of certain quirks or the identity of villains who are hiding in plain sight. And his martial arts expertise would make him a formidable opponent in battles against villains.
Tsuna's quirk, if we assume his Dying Will Flames are his quirk in the MHA universe, would likely be classified as an emitter type quirk. He could use his X - Burner attack as a long - range offensive move against villains. His hyper intuition could also be a part of his quirk, allowing him to predict his opponents' moves in battle. This would make him a valuable asset in hero teams, especially in complex battles where strategy is key.
One cool quirk idea could be 'Shadow Mimicry'. The user can blend into any shadow and move freely within the shadow realm, also being able to mimic the actions of those whose shadows they are in. It gives a lot of stealth and surprise attack possibilities in a fanfiction.
It can also expand the universe in terms of relationships. When Deku fuses with other characters, it can lead to different interactions with his friends, family, and teachers. For instance, his friends might be initially hesitant or overly excited about his new fused quirk, which can create various story arcs. Moreover, the fanfiction could explore how the fused quirk affects Deku's standing in the hero community, whether he is seen as more of a threat or a greater hope.
He could have a 'Ninja Arts' quirk. This quirk would allow him to perform all the ninja techniques he knows from Naruto, like the Rasengan or Chidori. His Sharingan could be an additional aspect of this quirk, enhancing his ability to learn and adapt to other quirks he encounters.
A quirk like energy absorption might be cool for Lucy. She could absorb different types of energy, such as heat, electricity, or even the kinetic energy of an attack, and then release it back in a more powerful form. This would give her an edge in combat and make her a formidable character.
One idea could be Batman somehow getting transported to the Boku no Hero Academia universe. He could use his detective skills and gadgets to help the heroes there. For example, he might be able to analyze the quirks in a way the local heroes haven't thought of before.
Batman would be an outsider with unique skills. His martial arts expertise and detective skills would set him apart. He could start by observing the heroes and villains in this new world, learning about quirks.
Well, Logan's powers would likely be considered extremely powerful in the My Hero Academia universe. His healing factor would give him an edge in battles as he could recover from almost any injury quickly. The adamantium claws would be a formidable weapon. However, he might face some challenges as his powers are more 'brutal' compared to the typical flashy quirks in MHA. He could be seen as a bit of an outsider in the hero community at first.