|As Lucina is a Falchion wielder, she can serve as both an effective healer and a fighter, or she could opt to improve her great offensive capabilities further.
Weapon: Falchion is Lucina's weapon of choice. When given its special skill, it will grant Lucina +4 to all stats if she has an ally next to her. This increases her bulk when defending against attacks, while improving her already great offensive stat spread. The Falchion will also restore 10 HP every other turn, improving her sustain, which is especially helpful in endurance styled modes. It can also help offset the self injury from Fury 3. Finally, it's effective against dragons, which means Lucina can help strike down any opposing dragons the player faces.
Assist: Reciprocal Aid is what allows Lucina to act as a healer of sorts, and is best used if she has Renewal 3 as well. With these skills, Lucina will heal 20 HP every other turn, as well as 20 HP at the start of each map for endurance styled modes. She can then proceed to share her pool of HP with injured allies and have her skills heal back up the damages for herself. Should the player use Lucina in other modes or feel like this is not necessary, then another Assist like Reposition can be used instead for its movement utility, helping Lucina move her allies around instead.
Special: Glimmer is Lucina's Special of choice, as it has a fast charge and helps her do even more damage. With Lucina's high Spd, she'll be able to double a lot of her opponents and activate it, potentially helping her secure the victory against her foe.
A Passive: Fury 3 is chosen as Lucina's A skill. It improves her overall combat performance as it grants Lucina +3 to all stats, although this comes at the cost of 6 HP after each round of combat. However, the self injury is offset by the Falchion's self recovery.
B Passive: Renewal 3 is an option for Lucina's B skill if she wants to serve as a medic for her allies, and should only be chosen if her Assist is Reciprocal Aid. With it, she can heal even more HP, and it lines up with her Falchion's self recovery, letting Lucina heal 20 HP every other turn, which she can then use to help heal her allies. However, should the player feel like this is not necessary, or use Lucina in less drawn out game modes, then Swordbreaker 3 is a great option for her as her B skill. This instead lets her duel with opposing sword users and come out on top.
C Passive: Spur Atk 3 is an option for Lucina's C skill, as she comes with it naturally and it can bolster the Atk of her allies. However, Lucina's C skill is flexible, open to be whatever the player needs. A buffing skill like a Drive or a Tactic skill could work well to help her support her team, but this is up to the player's team composition and discretion.
Sacred Seal: Attack +3 is an option for Lucina's Seal slot, as a simple attack boost is always nice. However, this skill slot flexible, open to be whatever the player needs, depending on the player's team composition and discretion.