While we can't speak for all Japanese people everywhere, Japanese society is generally welcoming of foreigners taking an interest in Japan and Japanese culture. Wearing kimono or other Japanese traditional dress, partaking in Japanese traditional arts, including a Japanese character into your novel, or writing your name in kanji will be welcomed by Japanese people as appreciation of their culture, rather than appropriation.
This is not to deny the existence of racism and cultural appropriation. We have found though that people coming to /r/Japanese asking if what they are doing is ok are asking from a place of respect and cultural sensitivity, specifically trying not to offend anyone. If this is you, then you're fine.
Japanese names
It is most common for foreigners to write their name as a katakana transliteration, unless their name is already written in Chinese characters (such as Chinese, Korean and Vietnamese names).
There is nothing wrong with writing your name in kanji instead or taking on a Japanese name, but you can expect to be questioned about this if you used your Japanese name in Japan while not obviously looking Japanese and/or not speaking Japanese natively. Japanese speakers generally will not know how to read your name if it's a kanji transliteration instead of katakana. But people won't usually be offended if you take on a Japanese name, including for your username or character in an online game.
Many people who take Japanese martial arts have been given, or wish to devise, a name in kanji, say to have embroidered on a belt or engraved on a sword. Go for it!
For more on the topic of cultural appropriation, see the following list of past discussions on the topic here in /r/Japanese.
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by gegegeno