Noble Phantasms aren't limited to a weapon, like mine is. The only limit is what that person's legends are.

For example, Robin Hood is a famed thief who stole from the rich and gave to the poor. He hid in the forest, and consequently, his Noble Phantasm allows him to summon entire trees. Think of how devastating it could be if that young boy were to combine his ability with that of growing trees everywhere.

[Little did Bedivere know, Q had been forced to do something like that not too long ago. But that would help paint a good picture for Dazai.]