What are your OC's Japanese first-person pronouns?
For the record:
"Watashi" and "Watakushi" are both gender neutral, and formal and very formal pronouns respectively
"Boku" is a masculine but rather boyish and casual pronoun (it's also used by a lot of girls in fiction, though there is the rarer Ore-Onna, a very masculine woman)
"Ore" is a lot more masculine and casual pronoun
"Atashi" is also very casual, but it's also very feminine
"Uchi" is similar to "Boku" IIRC but also originates from the Kansai region
"Ora/Oira" is very rural, gives a rather roughnecked vibe, IIRC it's mainly a Tohoku pronoun
"Wai" is basically the Kansai region's version of "Ore"
"Washi" is for older men
"Oi/Oidon" is a Kyushu pronoun, it's like the gender-neutral Kyushu version of "Ore"
"Jibun" is basically used by disciplined, physical people, like martial artists, athletes, and cops
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canon!Ryuji uses "Watakushi" in general talk, making him come off as rather overly-uptight. However, when he gets angry or emotional in general, he uses "Wai", which is the Kansai equivalent to "ore". Yes, he's still a born-and-raised Kansai kid.
AU!Ryuji uses "Wai" all the fucking time, making him come off as very informal, much like a stereotypical delinquent. However, when he wants to come off as polite, he uses "Wate", which is more like "Watashi" for the Kansai dialect.
Kenkashi Sendo follows a similar rule to AU!Ryuji up above: "Wai" in general, "Wate" for polite talk.
Ryoshi Makunouchi uses "Watashi" in general talk, but "Boku" in more casual talk.