Well that's the point of Nero, his devil harm its the base of his gameplay... is its principle weapon and he get more upgrate for that and this differ him from dante, If he gets more weapon like dante it will be always the same, and dante will became obsolete, that why they are different, dante get new weapon while nero get new harm and upgrade for his harmKind of wish he got more arms besides red Queen too
It's a great sword but cmon , one sword one gun
He needs more
Another style idea would be doppleganger since he is familiar with spectral projections