I duly searched baby name websites for the Japanese half of my real first name, Rei, which is from my grandmother's name Reiko. (The other half of my real first name is a pretty common name, often used for middle names these days) They said that Reiko meant "pleasant child" (-ko, a common suffix in girls' names, means "child").
|The kanji for "ko"|
So, then, "Rei" must mean "pleasant."
Except when it doesn't.
Japanese names are often written in kanji form; that is, in Chinese characters (though the Japanese read the kanji differently to Chinese people). But because a variety of kanji can be read in a variety of ways, the meaning of a Japanese name--even if it sounds the same--can be different, depending on the kanji that is used.
My grandmother's Reiko, for instance, originally used a character for "Rei" that she didn't like, so she used a different one. In my full name in Japanese, my character for "rei" isn't my grandmother's--in many families, a kanji character is passed down or used by successive generations. (On my grandfather's side, the kanji "ya" was passed down--Yasujyo, Yachio, Yajuro, Yasuhiko...)
My "rei" does not meant pleasant; it means mountain summit. Here are the different kanji you can use for "rei." Pieced together, my Japanese name is said the same way as one would say it in English, but the kanji meaning is "tranquil mountain summit" which is, um, well... I guess it's a personality to strive for?
But if you're searching on baby name sites for meanings for Japanese names, just know that the meaning there might only be the most common meaning, based on the most common kanji rendering of the name. Or just some uninformed meaning. Which is completely fine if you're just looking for a quick name to use for a character and you think you might want to go Japanese.
I named a character in Book the First Hikari, which means "light," which fit the character. I named a character in a short story Kimiko, because I wanted her to have a quick English nickname that she's known by while her full name often gets ignored.
If you're writing a story about Japan, with Japanese characters, then I expect a little kanji talk and some kanji research--a common conversation: "Wait, she uses that character for 'Yasu' in 'Yasuko?' Really? I didn't know that could be read like that!"
Popular Japanese Girls and Boys Names: 2015
Behind the Name: Japanese names