Some examples of such behaviour that you have experienced would be interesting. Even though I dislike many aspects of the culture, offhand I can only think of two Japanese people who have behaved in an underhand or manipulative manner toward me (that I've known about!) in 17 years of living in Japan.
Apologies for my late response. I stopped being so interested in Japan after I last posted. I'm not sure Japan and Japanese culture are right for me.
Maybe i'm just being sensitive, or maybe Japanese behaviour is too different from what I'm used to that there's bound to be a misunderstanding, I don't know.
I must mention I have never actually been to Japan. I'm only talking about my experiences with Japanese people in Europe and other parts of Asia i've visited. Below are most of the Japanese people I've met. Also I know of Japanese wives who married some of my friends for a while before divorcing.
1. The first time I met someone from Japan was a foreign tourist who was visiting a place I was local to. We were the same age and I was interested to meet him as it was the first time I had met someone from Japan. I showed him around the city, and I introduced him to the local food, while paying for some of his meals. He said that I was welcome to visit him in his hometown in Japan whenever I arrive. We exchanged contact information and when he was about to leave, I gave him a present of a bag of local fruits I had brought for him. The next day, I had realised that he had just left my gift behind. A few days afterwards I contacted him on the LINE app, but he never replied. I never heard from him again. I thought we became friends, but I felt a bit used.
2. The second time I met someone from Japan was a Japanese shop owner who served taiyaki and other japanese fast food. He seemed very friendly the first time I was there, but then every time I went there to sit down, order a taiyaki and talk to him (the table was right in front of him), he became more cold and less welcoming. I stopped visiting his shop because of a feeling I was unwelcome though I don't know why.
3. When I started learning Japanese very briefly, I booked a few sessions with a Japanese teacher. During our time together, she seemed really friendly and even allowed me to stay in her home afterwards for a while to eat an authentic Japanese meal she made for me. She was previously married to a foreign man but had since divorced him. She was really nice, asked a lot of questions about me because she was just very friendly and interested, and was really patient with my questions about Japanese. After I had finished my lessons with her, I spoke to her once more a few weeks later on the LINE app and she seemed really nice and friendly again. A few weeks passed, and I sent her another message with a question about Japanese. I didn't receive a response. A few days passed, and I sent another message and there was no response again. I was confused and I sent the Japanese question to the company she worked for instead. They responded, but asked why my Japanese teacher didn't answer it, and I said that she didn't seem to be responding to my messages. The next day she sent me a bit of an aggressive message to me, basically saying it was my responsibility to learn Japanese through practice. I wondered why she seemed very angry and why she was ignoring my messages. I didn't reply to her and I didn't hear from her again.
4. In this situation, I began talking to a Japanese woman on twitter. I have never met her before. We would often send messages to each other and she seemed really friendly and happy to talk with me. I sent her an e-mail asking if we could be friends. She never responded. I remembered all my previous experiences of Japanese people, and just assumed she was just initially friendly out of politeness.
5. There was a Japanese singer I really liked, but unfortunately she didn't speak english and I couldn't speak Japanese, so my messages to her were hard for her to understand. But there was a Japanese man the same age as me who was really friendly to me and would often translate my messages into Japanese and her responses into english for me without me even asking. He would always send me nice messages and ask how my day was. He asked me if I could be his friend and I agreed. One day I mentioned that I didn't have some of her merchandise. He responded by offering to send it to me from Japan. I was impressed by his kindness and initially agreed, but the next day I refused and I sent him a message that I couldn't give my full name and address to people on the internet. He seemed really understanding and friendly still, but when I offered to keep in contact with the LINE app, he never added me. Though he didn't seem like a bad person, I still wondered if we were still friends, or if we were ever friends at all, if he didn't want to contact me on the LINE app.
There seems to be a trend of Japanese people being really friendly, and then one day they stop being friendly and I never hear from them again.