Mavis was a non-carbonated chocolate drink sold along the Atlantic coast in Baltimore based Mavis Corporation candy shops in the 1920's and '30's. It was bottled at several locations from New York to Florida. One of the owners was Charles Guth who merged it with Loft Candy Stores. It was Loft who bought Pepsi-Cola out of bankruptcy in 1931 and bottled it in their existing plants and eliminating Coca-Cola from their menu. Guth introduced Pepsi in 12 ounce bottles for a nickle and the drink took off. Guth was later forced out and started Guth Cola. Loft, Inc. became the current day Pepsi-Cola Corporation.
It is a complicated and interesting story that is fully detailed in the Pepsi History "Twelve Full Ounces" written by then Pepsi vp Milward Martin.