B!Lucina +spd - hp merged+1 (also +1 hp and spd)

I have this exact IV. Several things I can say:
- very good offensive potential. One of the fastest units in the game before considering skills and buffs, and a convincing amount of atk. If you're not going to focus her on support, I figure you're going to try to attack with her.
- her bulk is a little thin. Even with def+3 on Geirskoegul, she will not always be able to take two hits without a heal.
- certain swords are simply too fast for her unless she really goes for it, usual characters being Ayra and Karla, who often get into the mid to upper 40s. Support builds should strongly consider swordbreaker to deal with them, because even when playing support, she wants to be able to check the part of the weapon triangle where she has advantage.
- aether can be good on her, but you have to know what you're doing and account for the possibility that she can't take a second hit before activating aether.

Several ideas for you to work with:
- atk/def 2 seal. I tend to find that her def is just barely not enough to take the second hit, so even 2-3 points can make the difference.
- sturdy blow + swordbreaker + any seal, possibly spd+3. Very low investment.
- brazen atk/spd + desperation + flashing blade seal + moonbow
- swift sparrow + chill spd + spd+3 seal. She has 47 spd, which doubles most opponents, and if there's an Ayra or Karla on the opposite team, she will cut their spd by 7 which very often will suffice.
- from the work I did on self-sustaining duelist builds: something along the lines of brazen atk/def + wrath + noontime + atk smoke + spd smoke. She will heal a small amount, potentially small enough not to deactivate her brazen skill. Meanwhile, she uses spd smoke to compensate for not having boosted her spd using her A-skill.