They offer an all-you-can-eat menu for 15€ at lunch or 19€ at dinner (excludes drinks and desserts). It's written 19€ for lunch but it will be 15€ if you don't eat sashimi (they should do 13€ if you don't order any fish or meat...)
I really ate all I could eat (about 6 dishes) and there was no surprise on the check. I think their menu has an English translation (didn't pay attention) but in case it doesn't, the Italian text says you should make 3 orders maximum, although the way it's written I didn't understand it as a hard rule (you can order 3 times 4 dishes if you like... and can eat it, so that should be enough to anyone anyway), and that you can't order more until all the food ordered previously is eaten. Given the price I don't think one should complain about those common sense rules.
I think the staff is Chinese but the food is still closer to real Japanese food than in many "Japanese" restaurants in Italy. Despite the very low price I have no complaint about the quality. There are quite enough veg options to get full without ordering twice the same dish.
Their options for rice is either plain or non veg, but you can tell the waiter to bring you "rice, vegetables and egg" without the egg. I didn't try any soup but they have 2 veg soups. I was also too full to try any dessert but they have several veg options.
If I remember correctly, I had:
-(first round):edamame, veg gyoza, wakame, plain rice
-(second round)rice and veggies, veggie udon (called spaghetti in the Italian translation but it's really udon).
If I still had room for more I'd have tried the veggie tempura, or some veggie makis. Maybe next time in Rome.
I'm trying to think of cons about this restaurant, but there really isn't much that I could seriously criticize, given the excellent price, other than the fact they could indicate veg options more clearly. One could ask for more veggie Japanese dishes (and I know I've had veg dishes in Japan that weren't on the menu), but as I just mentioned there are more than enough options for someone with a lot of appetite to get full without taking twice the same dish.
Cons: Veg dishes not clearly indicated in menu