Perhaps that norm/pierce sword could start off as a Cutter, then require the 2* Thorn Blade to start that new line? The sword would function as a cutter for the basic attacks, and the charge could be a spin like the Calibur spin. The spin would be slightly weaker than normal, and the knockback would be slightly less like a CIV, but it'd shoot spines out in all directions like a giant lichen colony does (perhaps with less range than that, but, yeah).
I honestly find it disappointing that nigh nothing in the game requires something from a different line entirely to make, so a cutter using a thorn blade to lead to that new line would be interesting and unique.
That being said, if a new tier of equips come out, 6* or higher, I'd like to see weapons that require you to have more than one item to craft; like starlinvf's Ripjaw and a Fang of Vog making a sword that deals Normal, Elemental, AND pierce, with FoV's charge combined with the spike shooting.
Just brainstorming, here. If a new tier of equips come out, they have to be really, really hard to get... because, honestly, 5* gear is really powerful already. I personally wouldn't like it at all if they just added another upgrade to the line, like a 6* avenger or summat. They need to be unique, like combining two similar swords to make one that captures the best of both.
I'd call it an Ivy Lash Blade. It just fits.
Now for original content---
Piercing/Normal blade (can't decide if it would be better as a calibur or heavy blade line). A sword edge lined with jagged spines.
3* - Spine Back Blade - An old blade fitted with sharp spines along its edge. Advise caution while running.
4* - Wolf fang blade - A blade upgraded with alpha wolver fangs to give it a little extra bite. The wolvers never appreciated the joke.
5* - Ripjaw - A strong metal blade embedded with the glowing spines of the Snarbolax. Also fun at parties.