A Letter of Guarantee is a document that is necessary in order to obtain certain types of visa. This document is a promise between the guarantor and the embassy / consulate that the applicant will stay and act legally in Japan. It does not mean that if the applicant causes legal problems in Japan the guarantor is responsible. Ultimately, it is the one who did something illegal (the applicant) who will be held responsible.
However, the guarantor can also face consequences in certain cases. If the guarantor made a false statement in order to let the applicant enter Japan, knowing that the applicant’s real purpose of entering Japan was to commit crimes such as terrorism, human trafficking, or other types of crimes, the guarantor can be held criminally responsible.
In a lesser extend, if the guaranteed matters have not not carried out correctly, such as stay or return travel expenses or compliance with laws and regulations, the guarantor will end up losing credibility as a guarantor for future visa applications.
It is therefor important for the guarantor to make correct statements and make sure that they perform their duties as guarantor correctly.