What's so OP about it? I've just gotten one more copy of it when entered a wrong room by mistake
Not the SR sword, but the new one that's just been added (SSR).
It's got two skills:
Kikai Houjin: Kamui -- ATK+ (small) / HP+ (small)
Hikari no Koujin -- light ATK+ (small)
regular atk+ small is +10% at slv10, Kamui is a new skill and it's also been confirmed to be +10%. ATK+ (Large) is +15% at slv10, so just looking at that you'd think there's a 5% advantage, but since multipliers add in their respective areas and then are multiplied, the difference is even greater. This is a super simplified ver of the actual formula but basically you're looking at something to the ilk of:
DMG multiplier = (1+Houjin("Magna")skill) * (1+regular atkup) * (1 + Unknown)
One +15% magna weap will allow you to have 1*1.15=1.15 multiplier, with Kamui it becomes 1.1 * 1.1 = 1.21. Say you have 5 of each weap, now you're looking at 1*(1+.15*5) = 1*1.75=
1.75 vs (1+.1*5)*(1+.1*5)=1.5*1.5=
2.25. Oh, did I mention that you get a +10% boost to your HP for each sword?
The current ideal formula calls for ~1 standard weap / 1 bahamut weap / 1~2 Unknown / 6~7 Magna weaps, the new formula w/ the Schvalier weaps you will have 8-10 magna swords and a couple Unknowns and end up w/ a multiplier that's significantly higher than the current theoretical ideal, and an even bigger boost if you happen to have Zeus. You also end up w/ nearly double HP. Welcome to GBF, where game balance is secondary to developer favoritism and nothing gets playtested.