Guide
How the kit works
Start a fight with Swift Harvest when you can. It attacks an enemy and, after battle begins, deals Lightning DMG equal to 80% of Arlan's ATK to all enemies.
During battle, use Shackle Breaker against your chosen target. It consumes HP equal to 15% of Arlan's Max HP and deals Lightning DMG equal to 240% of his ATK. If he lacks enough HP, the Skill leaves him at 1 HP.
Pain and Anger increases his damage based on his current missing HP percentage, up to 72%. Use Frenzied Punishment on a target with enemies beside it when possible: it deals 320% of ATK to the main target and 160% to adjacent targets.
Lightning Rush deals 100% of ATK as Lightning DMG to one enemy. Arlan also restores 20% of Max HP when he defeats an enemy at 30% HP or lower. On entering battle at 50% HP or lower, he nullifies damage other than DoT until he is attacked; his chance to resist DoT debuffs is increased by 50%.
Build and why
Use four pieces of Scholar Lost in Erudition for CRIT Rate and more Skill and Ultimate damage. After the Ultimate, the set also increases the damage of the next Skill. Band of Sizzling Thunder is an alternative: it gives Lightning DMG and grants ATK for one turn after a Skill.
For the planar set, Rutilant Arena gives CRIT Rate and increases Basic and Skill damage once you reach 70% CRIT Rate. Space Sealing Station is another option, giving ATK and an extra ATK bonus at 120 SPD.
Choose CRIT Rate or CRIT DMG on the body, SPD on the feet, Lightning DMG Boost or ATK Percentage on the sphere, and ATK Percentage on the rope. For substats, look for CRIT Rate, CRIT DMG, ATK Percentage and SPD, in that order.
Game8 ranks Something Irreplaceable first among the listed Light Cones. It gives ATK, heals Arlan when he is hit or defeats an enemy, and raises his damage under those conditions. The healing helps survival, though restored HP reduces the missing-HP bonus.
The Unreachable Side gives CRIT Rate and Max HP, plus a damage increase when its wearer is attacked or consumes HP. On the Fall of an Aeon builds ATK when its wearer attacks and gives a temporary damage bonus after a Weakness break. Prydwen ranks On the Fall of an Aeon first, ahead of The Unreachable Side.
Leveling priority
Follow the game's order: level Shackle Breaker first, then Frenzied Punishment, Pain and Anger, and Lightning Rush. The Skill is your main single-target attack, while the Ultimate also reaches adjacent enemies. The Talent improves damage as HP goes missing.
For maximum ascension, you need 246,400 Credit, 50 Lightning Crown of the Past Shadow, 12 Extinguished Core, 13 Glimmering Core and 12 Squirming Core.
To level all skills to the maximum, you need 2,400,000 Credit, 5 Tracks of Destiny, 12 Shattered Blade, 54 Lifeless Blade, 105 Worldbreaker Blade, 12 Destroyer's Final Road, 28 Extinguished Core, 42 Glimmering Core and 42 Squirming Core.
Eidolons worth it
For damage, I'd consider Self-Sacrifice the most appealing upgrade. At 50% HP or lower, it makes the Ultimate deal 20% more damage and raises its multiplier against adjacent targets to the main target's multiplier.
Breaking Free is a useful defensive option: using the Skill or Ultimate removes one debuff from Arlan. Turn the Tables can prevent a knockout from a killing blow and restore him to 25% Max HP. Its effect is removed after it triggers once or after two turns have elapsed, so it is not lasting protection.
To the Bitter End gives the Skill 10% more damage at 50% HP or lower. You can treat it as a smaller bonus rather than a target on its own. Power Through and Hammer and Tongs raise skill levels; consider them less urgent than the effects you want from E2 or E6.
Teams
Give Arlan a sustain teammate so he can fight at reduced HP without relying entirely on his own recovery. Gepard is an Ice Preservation option; Lynx and Fu Xuan are Quantum sustain options named for him by the guides.
A buffer can help his damage. Asta is a Fire Harmony option, while Sunday is an Imaginary Harmony option. Pela is an Ice Nihility debuffer and fits when you want that role beside Arlan.
One team to consider is Arlan, Gepard, Asta and Pela. Arlan supplies Lightning damage, Gepard takes the sustain slot, Asta is the buffer and Pela is the debuffer. Adjust the sustain slot if keeping Arlan alive is more important than keeping his HP low.
Common mistakes
Don't treat 1 HP as a safe target just because Shackle Breaker can leave Arlan there. The missing-HP bonus comes with the risk of being knocked down, so watch the enemies and your sustain before using it again.
Don't assume the entry protection stops DoT, or that it lasts for the whole battle. It applies when Arlan enters at 50% HP or lower and ends when he is attacked.
Don't ignore set thresholds. Rutilant Arena needs 70% CRIT Rate for its Basic and Skill damage bonus, and Space Sealing Station needs 120 SPD for its extra ATK. Check your stats before counting on either effect.
