entrance exam, combat training & usj attack
summary season one is a standard first season of any show, focusing mainly on getting you acquainted with the characters and the world mha is set in. izuku midoriya, the main character (duh), meets all might (aka the number one hero) during a chance encounter at a villain attack and asks if he can become a hero even if he doesn't have a quirk. he ends up inheriting one for all from all might, and trains so his body will be able to handle the quirk. he applies to ua, the most prestigous hero school in japan, and gets in through "rescue points" alone (points awarded for rescuing friends/defeating low-point villains in the entrance exam). the combat training arc is just how we get acquainted with the characters of class 1-a, as well as the lore between bakugo and deku (i love bakudeku im sorry..). bakugo and deku have a crazy one sided rivalry going on, which is made clear when the pair are pitted against each other in combat training.
the usj attack arc is undoubtedly my favorite arc just due to it being tomura's first real appearance in the show; while training at a far away location designed for practicing rescues in natural disasters and other catastrophic events, a group of villains appears. many of them are pretty low-level, allowing the students of class 1-a to easily defeat them. however, their homeroom teacher aizawa is pitted against the leader of the group, tomura shigaraki, as well as the anti-symbol of peace, the bioengineered nomu. luckily, all might saves the day.
my opinion i skipped this season during my first rewatch of the show, but now on my second rewatch i feel that it is pretty important, duh. the scene of deku trying to help bakugo as a child is really important to bakugos character but isn't brought up that often/shown again after this season. also, the prototype costume designs are so fucking silly. todoroki's stupid half ice half suit hero costume is so funny and i feel like horikoshi did a really amazing job with this season when it comes to writing 14-15 year olds to be 14-15 year olds. they all act and look their age which is something i've always loved abt mha.
tomura's usj look was so ugly though i hate to say it bc i love my man, but i found that although his dialogue quickly helps introduce him as the character he is (a man child, a gamer, etc), his design doesn't really show that as well. later on when his hair is longer and more overgrown i feel that it gives more of an impression of a man child who doesn't really care about little details if that makes sense. my other issue was that they glossed over everyone in the show besides deku, bakugo, tomura, and all might. which was just so buns... like i wanted to see more of the combat training pairings
i also dislike that, despite being such a high status and well built training area, usj is hardly mentioned or utilized after this season. i can imagine that there's a reasonable explanation for this, like it being unsafe or destroyed, but it's really not mentioned at all which is so weird

sports festival arc, hero killer arc, final exams arc
summary season 2 begins with the sports festival, which not only introduces todoroki's fire quirk but also the students of class 1-b, mei hatsume, and shinso who's last name i don't remember. anyways. the sports festival arc has three separate rounds; an obstacle event, cavalry battle, and 1v1 fighting tournament, with bakugo ending victorious (and tokoyami in 4th place, which is kind of crazy). following that is the work studies arc, where the class all split off to work alongside various pro heroes. deku works with gran torino (i really hated the work studies), todoroki works with endeavor, and bakugo works with best jeanist. however, iida works in hosu city in an effort to end up catching the hero killer, stain, who attacked his brother while iida was at the sports festival. he ends up encountering stain, and nearly dies, but todoroki and deku catch him. the final exams arc follows class 1-a facing both a written exam and a practical exam, with the threat of summer school and not being able to go to summer training camp being a threat if a student fails. while the written exam doesn't fill more than one or two episodes, the practical exam takes up the last five episodes. the students are paired up, each fighting a different one of ua's teachers; these pairings are strategically based on each student's weakness. while most of these weaknesses involve their quirks or abilities, bakugo and deku are paired up together due to an entirely different weakness: their interpersonal relationship. once the exam is over, it's announced that the threat of being unable to attend the training camp was a lie, and all students of class 1-a will attend regardless. to celebrate, they all go to the mall to buy things they might need for the 1 week long camp, and deku ends up meeting shigaraki.
my opinion this season was hit or miss for me. i believe that s2 is also the first season to have a filler episode, but i just skipped that one during my rewatch. when i began mha this year, i started with s2 and i found it a lot more enjoyable, so i could have just disliked it this time around because shigaraki didnt appear much in it and there was a bit too heavy of a focus on izuocha in the final exam arc.. nonetheless, the sports festival arc remains one of my favorite arcs in the entire show. i found it really entertaining and thrilling to try and guess who might win, and learning about other character's quirks was cool. it was one of the arcs involving all of class 1-a where bakudekutodo didn't outshine everyone, at least for the most part. we got to see tsu and ochako and mei really thrive, which is rare considering horikoshi tends to not gaf abt his female characters. bakugo being given a muzzle at the end of the sports festival was also like, one of my favorite parts of the season. i find that scene soo freaking silly
the stain arc was such a snooze. gran torino is ridiculously boring and unfunny in my opinion, iida was really stupid, deku was boring. it wasn't that interesting at all, and it kind of pissed me off how deku and todoroki just had to end up victorious. stain, however, i did like. his character is really cool, his design is cool, his quirk is cool, his motives are admirable. if i was in the mhaverse, i'd probably be a stain sympathizer, though i dont think his motives can really excuse murder. more importantly, though, stain and tomuras rivalry was TOOOOO GOOD. i wanted them to kiss sooo bad. they were such good yaoi.
the final exams arc was fucking crazy. i found the other battles soo boring besides tokoyami and froppys, but bakudekus battle? so crazy. i am a bakudeku shipper forever but i feel like all might's commentary about the two of them was just so??? like they are actually in love and this arc made that so, so clear. lastly, encounter. oh my god. encounter is my favorite episode of the whole season (sorry im so biased)... i can't think of a better way to reveal tomura's face? it was soooo good i could go on and on about it, but regardless!