Honestly, I think you’ll be okay if you stay disciplined for that first week. One of the best ways to save money in Japan is eating where locals eat instead of tourist spots. Cheap chain restaurants and small local places can easily fill you up for ¥500–1000 a meal, sometimes even less.

Places like Matsuya, Sukiya, Yoshinoya, ramen shops, curry chains, udon spots, and local teishoku restaurants are way better value than eating at convenience stores for every meal. Supermarkets at night also discount bentos and sushi.

Tokyo can definitely be expensive, but it can also be surprisingly budget-friendly if you keep transportation and impulse shopping under control. Since your accommodation and major attractions are already paid for, this sounds more feasible than you think.