later on, some SSR weapons get the ability to break a 4th time. this increases max skill level to 30, increase max lv for the weapon itself to 150, and adds a 2nd effect...
in the case of vritra's weapon, it's gonna get both a defender AND assault... making it a really good dual weapon (plus the stats on it is rather strong).
but, that 4th break is gonna require orichalcum from what i heard... and those.... good luck with that if you can't clear accessory quest 4 with ease, cause you won't stand a chance on Guild Order runs unless you can