In japan, most of the Kei cars are made in collaboration with other Japanese motor companies.
Suzuki alto is being manufactured by mazda as Carol, Nissan pino with same features. both uses Suzuki K6A series engines with a capacity of 657~658 cc that produces 54 Hp providing an fuel economy of 17.2 ~ 19.8 km/l.
similar cases are Suzuki Wagon R which is manufactured under the tag of Mazda Az wagon with same specifications, shape and size.Other examples are Mitsubishi ek wagon as Nissan otti, Suzuki moco as Nissan Moco etc.
In my personal opinion,the seating and driving experience shows that Mazda Carol is far more comfortable as compared to Suzuki alto.