@gingermarie If I were in your shoes I would:
Identify the causes of my burnout, and if it's the job itself make the move.
Keep it first and foremost that knowledge of Japanese culture/family/internship life is different from Japanese corporate work culture and its translation into the gaishikei work culture of the company you'll be entering, and is also different from knowing how to live long-term in Tokyo.
You'll continue to be expected to be fully culturally Japanese and to have uncanny valley moments when any of your behavior deviates from the norm without people either understanding your American side (regardless of whether you have chosen to divulge it) or deviating from the norm themselves, and the huge influences this can have extends even to simple things like how you dress or physically move about the office.
Be prepared to leverage my existing networks and social safety nets, and also learn how to find the haafu and international school kid communities if I'm ever in need of more support and quicker friendships.
Not sure if you've experienced the horrors of making new friends and building social circles as an adult yet so dropping this here. Tokyo can be a lonely place!
Try and figure out what subcultures fit my lifestyle and how to find them.
You mentioned frugality but not much else; there's very wide and deep range of chasms dividing parts of Japanese society with the psychological and economic facets having deep-rooted geographical echoes. Sharehouses (small and massive) and roommate seekers are becoming more and more common though if you want to replicate that part of your current lifestyle.
Figure out if I'm cool with Japanese food all the time or will want to replicate American food/beer/social experiences more often than not cause that'll run up the bill.
Figure out how important romantic relationships are to me and if it's important then realize it could be magnitudes more difficult to form them without some massive compromises on expectations or the pool size of potential partners or adaptations to Japanese (Tokyo) courtship practices.
(On that note, if you're straight I'd also take advantage of the massive gender-based pay gaps/career trajectories and societal recognition of those gaps to get some rich experiences paid for by random dudes while remaining frugal just to see what it's like if you haven't before, cause Tokyo men at the upper end of the income pool (trading companies, consulting, faang included) seem to have zero problems shelling out for expensive dates especially early on in a relationship.
Also I would be careful to keep up my American caution at all times when drinking/walking back home/on all day dates because there's way too many stories about SA and stalkers and what is often a complete lack of legal and institutional support.
If you use them currently, say goodbye to drugs if their use will have any impact on the visa status you utilize to enter, or be extremely comfortable with the risks of accessing those subcultures here or talking openly about your experiences with them in mainstream settings.
Consider continuing to fund my IRA etc since I'm over the income exemption, also plan for account access and address usage after my parents move to Japan.
Make sure you also know the rules and workarounds for Americans looking to invest in foreign markets and if there's any potential for investments you make as a Japanese citizen to run afoul of the US tax laws that cover you.
Have an additional emergency fund with at minimum an amount of cash sufficient for a last minute round trip flight at all times, for use for important friends and family.
Open an American credit card or two with amazing bonuses for credit card churning right before moving, since Japanese cards offer nowhere near the benefits of American cards and you can essentially swap out a portion of your USD emergency fund while building a Japanese one, plus hedging some bets if the yen recovers suddenly.
Make a game plan for keeping in touch with the people most important to you in the US, friend- and also career-wise. The latter is important because you're already impressing people in the US and it'll help maintain other opportunities whether you decide to go back or become the go-to person for X in Japan/APAC regional manager etc.
Prepare to maintain my English-language information flows, since so much of what happens in tech is communicated in English and the time lags can be massive, while also quickly identifying key sources of information about tech developments and adoption in Japan/general developments in society. (Includes getting a library card and setting up online access for borrowing free English ebooks.)
Read up on and understand the rights you will have as a worker in Japan, including how hard it actually is to fire someone and the $$$ the government will give you in between jobs if you ever get fired, take a mental health break or decide to retrain.
Understand the Japanese medical system (including dentistry and optometry), both how/when to use it and (hope I'm remembering this right) how to apply for government coverage of medical expenses over the yearly threshold, which I think is like $2000/year.
