As someone that has been living in Japan for a long ass time, I can comfortably say that he will not last a year. He will probably be getting at most ¥280,000/month (~$1800) and most of that is going to go down the drain. If the company is renting him an apartment, that will be like 1/3 of his salary and many companies will work hard to jew foreigners out of money along the way. I can't remember but I think he said he was going for a teaching position, which means that realistically his salary will be around ¥250,000/month. If the place offered him a contractor license, that means he will have to cover healthcare, social security, and taxes all out of pocket. Companies that hire foreign workers also pad the salary to control them as well. They may start the base salary as legally low as it can go, like ¥175,000/month and then add things like "housing allowance" and "attendance allowance" to get it up to the ¥250,000/month stated on the contract and then if you miss a day of work (maybe even late to work) or the company apartment is a mess, they will deduct that from the salary. Not even getting into the work hours, legally a Japanese company can work someone without overtime if the business has less than 9 people or something like that. So let's say that he is working for a company like NOVA or Kids Duo, which has 1000s of employees for the company, hires him and puts him in a location that only has like 8 people working there, they can work him for like 45 hours a week without overtime pay, that would mean the 40 hours for the week AND a Saturday. If he complains about it, then they can just fire him since he would be on a contractor agreement and hundreds of people like him are literally coming in to fill those positions.
Japan is also a place where you HAVE to assimilate. If you don't know the language or how to work through the bureaucracy, you're going to have the worst time. They also don't appreciate people like him. No one wants to be friends with a fat, bearded white guy that likes anime and videogames, they are a dime a dozen in Tokyo now which will make his life even harder because people hate them.
But if the job and society don't beat him down, the cost of living with a shit salary will.