(Sorry if it’s in the wrong sub cagetory!)
Long story short, I got 7 Brave Lucinas… All of them with pretty bad IV’s. I just got a Brave Lucina today and I’d like to finally begin merging them… Which one should I merge them to?
1: -atk , + def
2: -atk, + spd
3: -spd, + res
4: -spd, + atk
5: -spd, + atk
6: -spd, + hp
7: -def, + res
Or should I just wait again for the next banner with Brave Lucina?
+SPD is pretty good as you may want to focus on her supportive abilities with [Geirskögul (+eff)], so I’d go for it.
You don’t need to wait for the banner to return, even if you regret choosing +SPD and want +ATK later merges will carry over if you “merge” all onto the different IV copy so you won’t lose anything regardless of your choice.
Go +SPD
Okay, thank you for your input!
+Spd can save her from being doubled as well as helping her when she does have to fight.
+Atk is also quite good to potentially soak a Chill Atk, but it doesn’t help her survivability at all.
Personally I’d go +Spd 
+spd
I’ve merged mine up slowly,so I’ve had the opportunity to use +hp and +def for awhile,but after switching to +spd with the last merge it really opened up more build opportunities for me since her statline is decent with okay spd and a boon with max merges is more reliable in denying doubles.
To really answer this question, you’re going to want to plan out who you want to use Lucina with, because you may be able to soak chills with one iv better than the others for that particular unit.
+spd is by far her best boon. Remember that when you merge, the bane disappears, and so the -atk bane on your +spd B!Lucina doesn’t matter at all as soon as you merge.
Having pondered the same question with a +7 B!Lucina and having seen a fully finished B!Lucina (merges and flowers) I can definitely advocate for +SPD; you’re generally going to use her in a supportive capacity and you’ll definitely appreciate the extra SPD to work with when using and building her in whichever fashion (essentially, reflecting what everyone before me has said).
Avoiding to be doubled is her priority I think.