Highest protein-dense, low fat, raw, plant-based ingredient?
I'd say young green peas are a good bet. They belong to the broader bean family, which is in itself very high protein. However, many beans can't be eaten raw, be it because they can't be digested  or are even a bit toxic when raw. Young green peas on the other hand have a good amount of protein while they still can be eaten raw, about 2.5-6g per 100g, depending on the variety, according to (German) Wikipedia (English Wikipedia gives 5.42g). They are low fat, too, but a bit higher in carbohydrates. 

However, this is still not that much protein compared to the recommended 45-55g you need each day. You'd have to eat at least 1kg of green peas to get your daily recommended dosage of protein. So I'm not sure if it fits your needs. 

That said, not knowing why you want them raw, I guess you could also have ripe, dried green peas (even higher in protein: ~25g per 100g) ground into a flour and mix it with water to create a mash (this would work with other kinds of beans as well, although I'm not sure which ones can and which ones shouldn't be eaten raw.) This would certainly qualify as high-protein, low fat, raw, and plant-based, but I'm not sure it would be a culinary bomb.