Well, one can only guess right? Izuna is a mythological mountain. Tajima is a rice paddy something (can't remember) but what these names have in common is nature and/or mythology. Let's go with Natsusa, Ugaya and Amida. A warrior, god associated with young death and one who writes in the sand. I chose Ugaya (a famous mythological warrior) because as we do know, they were child soldiers and being a warrior was venerated. Amida is the Japanese god turned to when someone dies young, and we know he died young. Natsusa (one who writes in the sand) because when you write in the sand, it's ephemeral. It is washed away and no longer remembered. Madara only remembers Izuna. We can say that he died quite young. Ok, I hope you're satisfied with the names. All are pretty symbolic one way or another and hold a lot of meaning to the boys. Also, all names end in 'a'.