Hi there
As underligned in the notice, this game is subject to regional activation restrictions and can ONLY be activated/purchased from european countries. see details here : https://uk.gamesplanet.com/community/sekiro-shadows-die-twice-steam-key--3899-1/discussions/155257-sekiro-regional-restrictions-for-activation-on-steam
Note that the version sold on our us portal can only be activated in North america https://us.gamesplanet.com/game/sekiro-shadows-die-twice-steam-key--3899-1
So I'm afraid we cannot offer any activation in Japan, sorry about this