Japanese illustrator with a nice round sense of form, a bit like Izumi Takemoto. His work has appeared outside Japan in the western released Cacoma Knight, and Kendo Rage. Employee, or former employee, of Datam Polystar.
There doesn't seem to be one particular name to call them. In Japanese it would be 清水あの ? But it never seems to be written that way in this person's case. Typically fully or partly Latinised, or even as Alta Shimizu. So perhaps it's only a pen-name?
Some examples of their work