Travel, Teach, Live in Japan
1. Don't Be Aggressive - Japanese are inherently "shy" when it comes to foreigners. Japanese society is very rigid and follows strict social traditions based on honor, pride, and respect. Trying too hard to pursue a Japanese friend who isn't interested in you will never work. In fact, the best way to win over a Japanese is slowly over time, by showing them you are not simply interested in a sexual or "showing off" type of relationship. In other words, don't ask for phone numbers the first time you meet someone!
2. Don't Talk about Anime/Manga - Contrary to popular belief, most Japanese people are not addicted to anime or manga. In fact, the word "otaku" which refers to someone who is disturbingly addicted to this media (along with hentai) is derogatory in Japan. If you are an "otaku" type of person, you will probably scare away most reasonable Japanese people. They will likely think you are creepy.
3. Don't Try to be Japanese - Also contrary to popular belief, you will not "impress" Japanese girls or boys by knowing a lot of Japanese words and kanji symbols. They may pretend to be impressed, but mostly they will think you are creepy, once again. Knowing everything about Japanese history and J-pop singers and movies will just make you look like a weirdo to most Japanese. Remember, Japanese are interested in foreign cultures, so remain a foreigner! Learning fluent Japanese will only waste your time and break your heart. (In fact, most Japanese people secretly hate foreigners or "gaijins" who "move" to Japan for too long... they like visitors, or English penpals, but they hate "wannabe" ninjas.)
4. Have a Purpose for the Friendship - Japanese people, even the ones who are super interested in foreigners or English, still prefer to have some sort of purpose to their relationships. If they are studying abroad in America, for example, you guys can help each other with moving or errands, or practice English together, or have fun together if you both don't have many other friends, etc. This type of friendship, where there is mutual benefit, has long term potential, even when the Japanese friend moves back home. However going after Japanese just because you are "interested in their culture" doesn't really sit well with Japanese people.
5. Find Japanese who are Internationally Minded - Believe it or not, even though Japan is a super modern country, many Japanese prefer to keep to themselves. They buy Japanese products, watch Japanese television shows (mostly), and desire Japanese spouses and friends. It is what they know and trust. However, things are slowly changing, and there are many Japanese who have become keenly interested in learning English, working or living in other countries, or even dating a non-Japanese person. These are usually the Japanese people who are already more outgoing or "abnormal" in their own country. Thus, these type of Japanese may be overly flirty, goofy, or crazy... but at least they are interested in you!
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