Yakult | rdtlsbooru

A Japanese brand of cultured milk; a probiotic. It is fermented with the same bacteria found in DanActive (Actimel), called lacticaseibacillus casei.

Often associated with Suigintou from Rozen Maiden, due to a scene in the anime where she taunts an old man and asks him if he's had his lactobacillus drink today.
Splatoon has a weapon name and design inspired by the drink, the Reef-lux 450.

Edit