The short answer
Japan's app market has high ARPU but fierce competition. Run UA budgets by cohort LTV and payback period rather than download counts.
Looking only at cost-per-install (CPI) inflates numbers with low-quality users. Tracking post-install retention, monetization, and LTV by cohort reveals true efficiency.
Combine search, social, video, and rewarded channels, comparing user quality across channels by LTV. Account for measurement constraints like SKAN.
Localization drives UA efficiency. Localizing the store page (ASO), creative, and onboarding to Japanese language and culture improves both conversion and retention.