Pokémon Box Link is an item in the “Unused” category (Key Items).
In-game descriptions
| Let’s Go, Pikachu! / Let’s Go, Eevee! · Sword / Shield | --- |
|---|
Where to find it
Not placed on the atlas maps (so far: Red/Blue and Generation 3).
Sources : PokeAPI (items, item_flavor_text, machines) · atlas · pokeemerald species_info.h