You can use an item called "Cron stones" to avoid the item downgrading or the accessory from exploding and downgrading instead. BUT if you use crons you gain nothing for your failstack
Anyways, there's a class called Shai that's like. Weird. She heals, she buffs party members and is a tank with shit dmg. And she has a "Sol" for what's usually a 3rd weapon. You cannot sell a Sol. You cannot buy a Sol. You get 2 when you do a class-specific class and it's up to you to improve it