Longevity gives the alliance political gravitas

How long could the alliance last before the British and Japanese empires came to blows?

It could fail quickly or last for decades; every additional year gives it status and relationships that make a rupture harder.

Ceremonial ties, including Japanese imperial attendance at a British coronation, could reinforce the idea that the two monarchies are partners. Such public connections would make attacks on British interests harder to justify in the emperor's name. The longer the alliance lasts, the more status it acquires, while Britain can also be perceived as a source of support and a buffer. Territorial ambitions and political factions could still overpower that accumulated goodwill, so the alliance's longevity remains uncertain.