Worth skilling 5* with dupe?

[GotLoveForAll]

I just got my 2nd Fir. Is it worth to skill my 1st with her or skill level with crystals and keep the extra girl around?
Also just got dupe German Iris on a 11x roll.

[Unregistered]

You may want to wait until the bond crystal system gets implemented, since you can never have too many of these and fusing golds/rainbows rewards a good number of them.

Otherwise, gold are usually better off being fused. Rainbows are the same, unless you're a hardcore min/maxer and want to hit 720k power when blooming comes out.

[Zandel]

I just got my 2nd Fir. Is it worth to skill my 1st with her or skill level with crystals and keep the extra girl around?
Also just got dupe German Iris on a 11x roll.

If you just started the game you might get some value from lvling them a bit but to be honest it's better just to merge them into your main girl of the same name until you have 5 skill and 4 equip unlocked. 5* come thick and fast, there are 5 on perma reissue and another on reissue plus the current event girl and they add a new event and a new reissue every 2 weeks so you should get 20+ 5* very soon and not need any dupes.

[GotLoveForAll]

You may want to wait until the bond crystal system gets implemented, since you can never have too many of these and fusing golds/rainbows rewards a good number of them.

Otherwise, gold are usually better off being fused. Rainbows are the same, unless you're a hardcore min/maxer and want to hit 720k power when blooming comes out.

I have no idea what Crystal System or Blooming is xD

[Unregistered]

Bond crystals are obtained by fusing bronze+ units. They allow you to buy second affection items and (in an indirect way) 7.5% rainbow/92.5% gold tickets. They are currently only available on DMM, but should eventually arrive to Nutaku.

Blooming is like another level of evolution. It gets you an increased level cap, stats, new abilities, the works.

[Drip]

Simply put: it's probably better to use your low level Fir as material for your high level Fir.
The only exceptions I can think of:

1) Your higher level Fir is about to reach maximum level soon, meaning you will evolve her soon. In this case, it's slightly more efficient to combine the two immediately after you evolved your high level Fir, since the experience gain from using girl cards is so little, that it's only noticable at low levels. (Evolved Fir would be back at lvl 1, to start leveling again, but with way better stats and an extra passive ability)

2) You don't have enough gold and silver girls yet to fill all your squads. In this case, it may be worhwhile to keep both for a while, but keep one of the two below lvl 20. Eventually, you'll want to merge her into the higher level Fir, because you simply found better girls to put on your teams. Leveling them to 20 is cheap, beyond that is noticably more expensive, and because of that, a waste of resources for this kind of place-holder dupe girls.