Don't boast, don't talk too much about yourself
What not to do when dating a Japanese woman?

As Westerners, we tend to put a lot of emphasis on persuasion, eloquence and talking while Japanese tend to be suspicions of silver-tongued verbosity and tend to see it as a means of tricking and taking advantage of others.
Humility is your best friend in life... and in you relationship!
On the other hand, girls like to know a little bit about you so they can understand what you are talking about sometimes. In addition to making you a much more desirable conversationalist, it will make you seem more mysterious to not share too much, which many women find attractive. Get a basic idea of what's going on in music, sports, and politics.
Be humble, don’t talk about yourself too much and be sure to keep a balanced conversation.
Remember, confident men don't feel the need to boast.