Luartha (Winter) is a limited-time unit centered around Christmas, similar to the other winter units. She's a crit-based damage dealer with a unique main job that almost makes her play like Rangers (except without a long-range normal attack), poking from afar and softening them up in the process with single target attacks. Despite the medium damage multiplier, she has access to Self-Sacrifice and some crit-related stats from her passives, allowing her to hit pretty hard with every attack.
Her signature move, Binding Javelin, has a range of 5 (6 with a passive) and can decrease healing power + a decent chance to inflict Immobilize if it crits. Combined with her Masterful Melody, which is a triple buff in 1 convenient ability, it essentially gives her the advantage when it comes to a ranged fight as long as she has the AP for it.