|With Weapon Refinery and the introduction of premium staves in update 2.0, Lucius can brandish together a simple but deadly set comprising of most of his default skills.
Lucius is the sole native Pain+ user that can be obtained at 5 star rarity, unlike Azama. Also unlike his fellow monk, Lucius sports a decent and certainly usable base 32 Attack, enabling him to deal damage outside of Pain's passive corrosion—while also giving him the power to actually finish off foes in emergencies, no less. To maximize Lucius's ability to wear down the opponent as well as nearby enemies, Pain+ must be refined to its Dazzling version. This variant of Pain+, together with Wrathful Staff 3 and Pain+'s ability to stack with Savage Blow 3, are combined to create a beautifully disgusting strategem: the ability to deal free damage and bring most of the opposition to their knees in the blink of an eye. As a note, as long as Pain+ is refined to its Dazzling version, Wrathful Staff is not actually necessary to achieve this set's goals, though it is not nearly effective without it.
The numbers almost speak for themselves: nearby enemies will take a hefty 17 damage if Lucius equips Savage Blow 3 in his C skill slot alone, and will take even more depending on the Sacred Seal version's current level. With maximum specifications, these enemies will take 24 damage, which is essentially 2/3 of a typical mage's HP and nearly half of an armored unit's. Meanwhile, the target is faced with a decently powerful magic attack that ignores weapon triangle affinities, and further suffers Pain damage if they weren't already defeated. Like most offensive healers after the update, if Lucius is supported by teammates with Reposition, he can potentially—for lack of a more defining term—cheese most matches simply by ignoring counterattacks and picking off units without worry of Vantage or other forms of reciprocation. In other words, you're looking at a free win against Armor Emblem (particularly among other teams), many of its units which have low Resistance and otherwise no defenses against magic attacks outside of Distant Counter.
There's really no need to replace Martyr+. It comes naturally with Lucius's base kit, heals Lucius himself, and restores a hefty 21 HP at minimum—not counting Imbue, possible increases to Lucius's Attack stat, as well as sustained damage from tanking magic attacks (which Lucius can certainly do in emergencies thanks to his high Resistance). Lucius's Special slot is perfectly flexible: several suggestions include Imbue to heal a larger amount of HP in emergencies, or perhaps one of the Balms for further stat boost coverage.
Lucius's A slot is reserved for a flat stat boost. If Lucius has a speed boon, it is recommended to further amp it up with Speed +3 to avoid doubles from opposing mages while being able to double slower foes himself. Otherwise, Attack +3 is a fantastic choice for further damage and slightly adding to Martyr+ healing. If the additional damage from Savage Blow seems excessive or overkill, Lucius can opt to use another C passive skill, such as Hone Atk 3 to support his teammates. Alternatively, his Sacred Seal slot can instead be taken by Distant Def 3, enabling him to go toe-to-toe with opposing magic users universally.