Adaptational Badass: Far more capable and cunning here compared to his canon counterpart thanks to his Judgement training; the ODD helps too.
Adaptational Personality Change: Subtle, but in the main series Touma is noticeably paranoid about accidentally showing his memory loss to anyone, here his close friendship with the girls largely make this a non-issue making Touma less neurotic as a result.
Mikoto gradually drops her early rivalry with Touma in place of a growing friendship and possible romance, something which doesn't exist in canon until later on in the story.
Kuroko Shirai hates him in canon, but here she comes around and welcomes Touma as a close friend and partner.
Accelerator and Touma never meet each other throughout the original series, right up until the end (save for some moments) but here they were Childhood Friends who due to a traumatic experience drifted apart, until Yuri Suzushina forgot about Touma as he sinks further into the darkness.
Mugino Shizuri has no connection with Touma, nor do they even meet. Here, they're siblings, and eventually they reunite following the Sisters Arc.
Close-Range Combatant: Imagine Breaker lacks any ranged options, and his ODD, even with its javelin option is mostly effective at melee range, which puts Touma squarely into this box, although he can be creative enough to circumvent these limitations.
Deadpan Snarker: Incredibly witty and sarcastic, but he means well.
Determinator: Trying to stop him is like forcing a bull not to charge at anything red; if sufficiently motivated nothing short of death can make him back down of accomplishing his goals. Everyone acknowledges this as fact.
Fights Like a Normal: Imagine Breaker can only be used in close range, leaving him to rely on his combat training and ODD in conjunction with IB to even the odds against all manners of foes.
Humble Hero: For all his heroic deeds Touma is very modest, and would rather get into a fight with his classmates than take credit, even when the credit is justifiably due.
The Paragon: Touma's kindness has redeemed a couple antagonists onto the side of good, such as Accelerator, Mugino and STUDY.
Stone Wall: He lacks true superhuman strength and raw power, mostly relying on his own skills, the ODD, his incredible resilience, and Imagine Breaker when fighting superpowered foes.
Squishy Wizard: She's not particularly weak in melee combat, as she shows off a couple dirty fighting techniques here and there even in canon. However she is still flesh and blood, and her stamina and endurance aren't as impressive as Touma's.
Adaptational Nice Guy: Is a lot more friendly towards Touma due to their partnership, and her more questionable traits and flaws are downplayed/removed here.
Chivalrous Pervert: Kuroko deeply admires and lusts for Mikoto, and is not shy to display both affections to her (and sometimes at the same time) despite the inconvenience that ensues. Notably, her Adaptational Nice Guy upgrade in this story emphasises her "Chivalrous" side a lot more than her "Pervert" side.
Fragile Speedster: Her Teleport power makes Kuroko incredibly hard to fight, but one good hit's all it takes to take her out of the fight.
If It's You, It's OK: Has grown surprisingly receptive and accepting to the hypothetical scenario of a threesome with Mikoto and Touma, much to everyone's chagrin.
Ojou: Not as pronounced as the other students like Kongou due to her personality and occupation as a Judgement officer, but it's still present.
Ascended Extra: Unlike in canon, where it took until the Invasion Arc for him to become prominent, the Necromancer Arc does it for him, and his friendship with Touma maintains his continued importance in the story potentially later down the line.
Adaptational Nice Guy: Considerably becomes much more affable following his defeat by Touma and subsequent brain injury, though this only comes out towards Touma and the cast.
the author confirms the Official Couple of the story will be Mikoto and Touma.