There are several kinds of the first person(一人称) in Japanese. When Japanese learners start to work on this, they usually learn 私[watashi] first. This is the most common and polite one, that’s why. わたくし(watakushi, kanji is the same as 私) is too polite, if you ask me. However, if you are learning with anime, manga, TV drama, or whatever, you would definitely know more first persons such as 僕[boku], 俺[ore], あたし[atashi], or わし[washi]. Needless to say, some of them are men’s use, and others are women’s use.
Having said that, especially in anime a strange thing happens(well, a lot of crazy things happen anytime, if nothing else). I mean, even though she is a girl, she might be using ボク[boku] to address herself. Does this ring a bell to you? Grammatically and logically, this is definitely wrong, but for some reason this happens…If you encounter this kind of girl, you can call her ボク少女[boku-shoujo] or ボクっ子(娘)[bokukko]. ボク is mostly written as katakana rather than kanji. Maybe that’s because it would sound cute, I assume. Anyway, this type of girl could be innocent and adorable, and she might be lolita-looking and diminutive. Speaking of a ボクっ子, I can think of Ayuayu[Kanon], Mitsuki[Double Cast], Makoto[Idolm@ster], Ai-chan[Cat’s Eye], Kino[Kino no tabi], Utena, Hanyu[Higurashi no naku koro ni], Akane[Toki meki memorial 2]. Ugh, there’s too many, never ends. If she turns you on, you would sure have a ボクっ娘萌え[bokukko-moe]. But why? I don’t feel anything about this, so I wonder why this could turn you on? I guess a little girl who says boku makes herself more cuddlesome. Yes, of course this can happen in anime[二次元]only. I have seen a real ボク少女, but it was too painful to hear.
Meanwhile, there’s another type of girl. If she uses 俺[ore], she could be labelled as a 俺女[ore-onna]. We don’t say 俺っ子[orekko] for some reason. At any rate, 俺女 might be very cool and such a delinquent girl. ;^^ Yes, she tries to look herself stronger, but the real her is so lonely and weak…When she stops using 俺 and says 私 with a shy voice, she would show you her dere-side. Nah, this is an average クーデレ girl, isn’t it? Anyway speaking of a 俺女, I can think of Touma[Minamike], Kaori[City Hunter], Azumi[あずみ], or Kiyomi[Sotsugyou]. Even though they don’t say 俺, I would like to count Tomoyo[CLANNAD] and C.C[Code Geass] because there’s no feminine utterance from them like ～わよ[…wayo], ～のよ[…noyo], ～わね[…wane].
Too bad neither can turn me on!