Losing citizenship after naturalization

Hello everyone. I had a conversation with somebody lately. He told that some naturalized Japanese lost their citizenship after committing a crime. If the crime involves murder or terror, it is understandable. What about car accidents? What if someone got involved in a fight and had to hit someone to defend himself?
I am not sure if the person who gave me the information is right or wrong. Can you please confirm it? Don�ft hesitate to share any articles or sources about this case. Thank you.

Did the person you talked to provide any sources? I mean, they made the claim then you know, burden of proof and all. If they have led you to believe that the government could leave someone stateless over a minor crime like a traffic offence or a punch up in the street then they are either lying or very badly mistaken. Citizenship is citizenship.

Yes people can lose their citizenship from committing a serious crime such as terrorism if they have dual nationalities in overseas. However, I am so confused with your question as Japan currently forbids dual nationality. If a Japanese national was revoked their citizenship, they would be stateless. Everybody should have at least 1 nationality. I have heard that there are quite a few people who keep 2 or 3 passports secretly in Japan, which pisses me off. I believe those who commit a traffic offence would not lose Japanese citizenship.

Short answer - no. Another false statement made up out of nothing.
The Nationality Law applies and the case that would apply is A Japanese national shall lose Japanese nationality when he or she acquires a foreign nationality by his or her own choice.
Note the "own choice".

This took less than a minute to verify.

PR and visa holders would be can be deported.
Citizens cannot.

However, I am so confused with your question as Japan currently forbids dual nationality.
It is true that Japan does not allow dual citizenship. On the other hand, there are countries that forbid renouncing the citizenship. In these cases, the person will be able to apply for Japanese citizenship after submitting a document to prove the person has renounced his/her old citizenship. Technically, this is not a document but a paper signed that functions as an oath by the applicant. In this scenario, Japan can easily get rid of the person by simply deporting him to his original country. This is less likely to happen unless the person has committed it a serious crime.
The Nationality Law applies and the case that would apply is A Japanese national shall lose Japanese nationality when he or she acquires a foreign nationality by his or her own choice.
Note the "own choice".
I am afraid the law above may only apply to Japanese by blood (born Japanese) not those who were naturalized. There are always holes in laws.
I was a bit concerned but apparently. It seems the person I talked to has some false information. He may have confused PR with citizenship! I hope so.