Mikan is a 17-year-old high school student and the series' main character—the "atashi" in the title refers to her. She attends a public high school, which means dealing with a brutal daily commute, but she takes it in stride. She's the kind of person who's equally comfortable being girly or tomboyish, and she seems to attract funny situations no matter what.
Her core friend group is solid. Shimi-chan (Shimizu) is the calm, collected type who always has practical advice ready, whether it's about diets or family drama. Then there's Yukarin (Yuka), who's obsessed with karaoke and has basically dragged Mikan into appreciating cuter things. The two balance each other well.
Romance-wise, Mikan's got it bad for Iwaki, a typical pretty-boy type. She keeps trying to confess, but his best friend Yoshioka—who's been going to school with Mikan since elementary—constantly gets in the way with his annoying comments. To make matters worse, everyone around her, including her own mom, keeps pushing her toward Yoshioka instead. When she's looking at the two of them together, Shimi-chan usually misreads the situation and thinks Mikan's actually interested in Yoshioka, which doesn't help.
Academically, Mikan coasts. She's terrible at taking notes, sleeps through half her classes, and regularly oversleeps before school. Homework is basically a joke for her—she falls asleep doing it constantly and turns in incomplete assignments as a result.
Outside school, she's into karaoke, loves sweets (though she can't stand chocolate cake), and is genuinely passionate about teddy bears—both making and collecting them. She's part of the "Bear Brigade," her school's teddy bear club, alongside Rio (the rich, fashionable one), Nitta (nerdy but somehow manages a romantic life), and friends Kajii and Asada. They design original bears, put on performances, and obsess over expensive teddy bear merchandise.
Her actual dream is to become a teddy bear and/or fashion designer. According to her mom, she taught herself to sew buttons at three years old just by watching. She briefly considered becoming a breadmaker but dropped that idea fast.
Her biggest frustration is her mom's strict rules—curfew, allowance, fashion restrictions, and especially those sad boxed lunches she packs. It irritates her that her younger brother gets away with stuff she doesn't, though Mikan's usually clever enough to argue her case when it matters.
Content compiled by AnimeList.moe from publicly available sources.