I only remember it being available in Pokemon Box only if you pre-ordered it. And that was a long time ago!
Players who have Pokemon Sword or Shield save data on their system will be able to get Jirachi in Brilliant Diamond and Shining Pearl. Speak to the gentleman standing in the flower field near the southern entrance of Floaroma Town and he'll gift you the mythical Pokemon.
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Very recently. There were two this year, one the Decolora Adventures Jirachi, the other was Tanabata Jirachi. Both were Japan only, and had the special move Meteor Mash.
Serebii Eventdex - Jirachi
