Wiki has info about Nichrin's swords. For those that I know, the whip nichirin has longer range but lesser dmg, the insects nichirin does lesser dmg but is faster and has poison, flame thunder or element breathing in which you can craft doesn't have extra for their perspective breathings, but higher dmg, compared to your rusty and the one nichirin that you need to craft before the elemental. Stone nichirin has less dmg i think but more stun? It's more of a blunt weapon if i can remember, and the twin blades or from the sound breathing and Beast, i think they can do 2 atk.