Musashino Milk

Musashino Milk (ムサシノ牛乳) is a milk brand that was originally introduced in the Toaru Kagaku no Railgun anime adaptation and is later popularly used in the second Toaru Majutsu no Index anime adaptation.

Principles
Not much is known about the brand, however, several female characters seem to enjoy the drink in both franchises. Most infamously, it is often associated with female characters with large breasts.

The tagline of the product is: "When it comes to milk. It's gotta be Musashino!"

Big Spider Arc
In the anime adaptation, the milk is first introduced in the Big Spider Arc, where it is prominently featured as Kurozuma Wataru's preferred drink. Later, after Wataru comments about Konori Mii's large breasts, she states that it is because she drinks the milk anyway. The final episode of that arc during the epilogue shows Shirai Kuroko sipping the milk.

Poltergeist Arc
The milk is shown for the first time to replace coffee milk as Tsukuyomi Komoe's preferred drink after bathing in a bathhouse. Here, several characters, usually after a bath, drink the product. The product is then shown having been drink later in several quantities by Mii during episode 21 of the anime, after working all night. During the penultimate episode of the anime during the Poltergeist Arc, the milk is once again featured again, as Mii forces Misaka Mikoto and company to drink and eat up before going to the final battle with Therestina Kihara line.

Daihasei Festival Arc
Konori Mii, as usual, is seen drinking this milk product while joining Mikoto's friends to celebrate Kuroko's recovery.

Dream Ranker Arc
The milk is shown for the first time in Railgun manga. Here, Hamazura Shiage brings product for Kinuhata Saiai.

Daihasei Festival Arc
The product is first shown prominently in the anime by being the "health drink" that Fukiyose Seiri uses.

Toaru Kagaku no Railgun MMR
In the second special, Kiyama Harumi, Saten Ruiko, Shirai Kuroko, Misaka Mikoto, Uiharu Kazari, and Konori Mii, all indulge in the milk in an attempt to get larger breasts, whilst staring at the sunset. At the same time as this, loud and incredibly inappropriate burping sounds play.

Trivia

 * The name of the milk is likely derived from where J.C.Staff is located.