One common way for anime to introduce a new character is by having them transfer to the protagonists' school midyear. These characters can throw a wrench into the existing social order, become new partners in the fight against evil, or even become new enemies. Sometimes, they're even the protagonist, allowing viewers to observe the school environment through a fresh pair of eyes.
Who are some of the best new transfer students in anime? One great example is Homura Akemi of Puella Magi Madoka Magica, who first becomes a transfer student when her health forces her to take time off school, but then keeps doing it continuously as she goes through time loops, to ensure that she can stay close to Madoka. There's also Syaoran Li from Cardcaptor Sakura, who becomes one of Sakura's most indispensable partners, even if they don't exactly like each other at first.
Which ones are your favorites?
Ryuko Matoi is forced to transfer to Honouji Academy after starting enough fights to get kicked out of every other school in the Kanto region. Luckily for her, not only does her new school encourage fighting, but it also leads her to the answers she's seeking about who is behind her father's demise - and to a conspiracy that goes far beyond just her father.
After Shouko Nishimiya transfers into Shouya Ishida's elementary school, she faces a tough road ahead of her. That's because she's deaf, and her classmates are not understanding - rather, they start bullying her, forcing her to eventually leave the school.
Pretty much every Shinigami in the world of Bleach has enrolled in Ichigo Kurosaki's class in an attempt to either establish or maintain contact with him. This is amped up to a ridiculous degree when a filler character who is way too young to be in high school tries the same thing.
Although Yukihira Souma enters Tōtsuki Culinary Academy at the beginning of the first year of high school, he's still a transfer student because everybody else has been there since middle school. This, combined with the arrogant way he presents his cooking skills, makes it hard for him to make friends at first.