

CaloriesIn - CaloriesOut = WeightChange
Fat forms using spare calories. Any diet that involves eating fewer calories than what you burn will reduce your body fat.
As long as you have that part right, you are free to add any other requirements on your diet you wish.
It is the critical basis on why all diets work. One can eat as healthy as they want, but if they eat more calories than they expend, they will gain weight. Tossing aside such a fundamental concept is fraught. Instead, build upon it.
OP wants to design a diet that has the following requirements: reduce body fat, vegan, high-protein. Vegan limits it to plants, and high-protein further limits it to things like beans and tofu. Now, OP needs to figure out how much beans and tofu he can eat to achieve his goal, and this is where calories in - calories out becomes critical. Eat the right amount and the diet works.