According to Japanese Government survey, the highest number of foreigners was recorded in 2018 (source). There are more than 2.3 million of foreigners living in japan in 2016. Given the high number of foreigners living in Japan, there will also be different kind of people you can meet within this community. As a gaijin myself, these are some type of foreigners that I have met during my stay in Japan so far: ( does not include tourists )
As the name suggests, these type of foreigners are mostly just arrived in Japan. They are either came to Japan as exchange students, work, or long-term studies. Coming all the way from their own countries, new experiences and environments in Japan will (most of the time) excite them. You will see this type of foreigners taking pictures everywhere. It usually takes them 1-3 months for these newcomers to turn into either The Sensei, Bubble Dweller, Apartment Dweller, Foreign Ninja, or in some extreme cases, Weeaboo.
After staying for a while, finally the newcomer gained enough knowledge about Japanese culture. This additional knowledge turned the newcomer into The Sensei. This type of foreigners will usually stare into a group of foreigner tourists or other newcomers who are talking loud in non-Japanese language with disdain; thinking that `that is not how to behave in Japan`. The Sensei will often fix your Japanese, even the smallest mistake ( even if their Japanese is not completely perfect ). The Sensei will also prefer to hangout exclusively only with Japanese. Some of The Sensei I know are even more Japanese than Japanese people themselves!
While The Sensei is trying his/her best to be Japanese, the Bubble Dwellers are busy checking the internet trying to find nearby markets that sell foods from their own countries. Bubble Dwellers tend to hangout only with foreigners (specially from their own countries, and/ or speak the same languages). This type of foreigners may also have some Japanese friends (who are usually fluent in English ). Most Bubble Dwellers are not that good in speaking Japanese despite staying in Japan for many years! What is remarkable about Bubble Dwellers is their ability to survive in Japan with limited Japanese skills!.
After staying in Japan for a while, all those anime shops and Japanese foods do not impress the newcomers no longer. These newcomers choose to stay in their small apartment, watching youtube or anime alone, even during the weekend. Lack of social and Japanese skills force these newcomers to stay in each of their apartment, totally isolated from the outside world. In Japanese, there is a word hikikomori (引きこもり), which means adults who pull themselves from social life, confining and isolating themselves into extreme degrees. Not to be mistaken with the Bubble Dwellers, Apartment Dwellers will isolate themselves completely from outside world due to various reasons (mostly due to depression). Again, the purpose of this article is not to mock these Apartment Dwellers, do not let your fellow foreign friends (and Japanese friends) becoming an Apartment Dweller (hikikomori)!
After going through some phases, four types of foreigners mentioned above may turn into a Foreign Ninja. High Japanese fluency and enough social skills make this type of foreigner able to socialize with both Japanese or foreigners. This type of foreigner will not teach you how to be Japanese ( even though they are actually really fluent in Japanese ). This type of foreigner will never brag about their high Japanese skills, and they are usually hard to detect. But when you listen to them speaking in Japanese, you know that you are facing a true veteran!
Their deep interest into Anime, Manga, and thought about Japanese culture being superior may turn a foreigner into a Weeaboo. This type of foreigner does not necessarily can speak in Japanese. Most of their Japanese vocabularies are usually picked from Anime they watch regularly. Weeaboo prefers to hangout only with Japanese, not to be mistaken with The Sensei, the Weeaboo will not hesitate to show their deep love of some weird anime in public, usually in form anime costume and hair color that matches their favourite anime characters.