Forget the binary of low season or school calendar to determine the duration of the trip.
The real variable is the flexibility of personal leave, often a delicate negotiation within Japanese companies where long breaks are rarely taken consecutively.
People manage rest days like a capital, preferring several small escapes over one costly long trip, especially under productivity pressure.
For example, a colleague might prefer four long weekends with slightly higher airfare rather than a full week that puts their team under pressure, even in low season.