Kaisei
Your watch tracked the night. Kaisei reads it when you wake.
Kaisei is a private, on-device recovery and readiness app for Apple Watch owners. Every morning it reads the heart-rate variability, resting heart rate and sleep your watch already recorded overnight, turns them into one recovery score from 0 to 100 measured against your own baseline — then does the part most apps skip: it shows you every signal and weight behind that number, and says in plain words what kind of day it looks like. Six rooms hold the rest: Today, Trends, Health, Workouts, Journal, Profile. Your biometrics never leave your devices; there is no account and no cloud to log into. The gauge is the kanji 回 — regeneration — a squared ring that glows from ash-grey when you're depleted to vermilion when you're primed, and reignites each morning at today's score.
Six systems behind your morning score
Recovery, Every Morning
One score from 0 to 100, read against your own baseline: last night's heart-rate variability and resting heart rate, with the sleep score blended in at a smaller weight. The morning result stays in your history. Today's score keeps moving as daytime readings land, and a watch worn only by day still earns a Day score. Sleep with the watch off and Kaisei says so instead of inventing a number.
A Score That Explains Itself
The factor that moved your morning sits right under the ring — and every signal and weight behind it opens. From there: a plain-words read of the kind of day it looks like, an effort range that describes rather than prescribes, and a coach you can ask about your own data, free-form and on-device on Apple Intelligence iPhones.
Sleep, Stress, and Vitals
Deep and REM, efficiency, timing consistency, a rolling sleep-debt estimate and a wind-down cue — weighed against the sleep your body needed, not a flat eight-hour rule. Alongside them, a descriptive daytime stress read, cardio fitness, and HRV, resting heart rate, blood oxygen, breathing and wrist temperature against your own range.
Workouts and Training Load
Five heart-rate zones and a transparent per-session load estimate, live on the wrist while you train. Your week counted against the training days you said you keep, and your recent 7-day load against its 28-day average — shown only when the coverage is complete, and never sold as an injury predictor.
Journal, Readings, and Letters
Tag your nights — alcohol, late caffeine, medication, or anything you add — log how you felt, and backfill what you missed. Kaisei compares your own nights with and against a habit, and only speaks once it has enough of them. Two-week self-experiments, and a Sunday letter on the week you actually had.
Private by Architecture
No account, no login, nothing to sign in to. The app carries no networking code of its own, no third-party SDKs, no ads and no analytics. Your biometrics are read, scored and stored on your devices. Optional iCloud backup holds only your streak and tags. Export everything, or erase everything, in one tap.
Ready to start?
Get Kaisei for iPhone + Apple Watch