JessI inquired to the shop keeper,
"Shop keeper, sell me your biggest Pikachu plushy."
The shop keeper calmly replied, with a smirk on their face,
"You cannot handle my biggest Pikachu."
(In other terms, it was not for sale 
)
It appears to be an OG style Pikachu plush; the bigger friend that appeared in early comics and card/game designs, before Nintendo slimmed them down. I cannot find any for sale online (in English at least), seems quite rare.
