Trait rerolling starts at the Traits NPC in the Upgrades area, where the menu lets players select a unit and spend Trait Shards. Auto Reroll works after you know the result you are keeping. If you turn it on without a target, the menu can spend shards quickly and leave the unit with no better role in your team.
The unit comes before the trait target. A temporary filler unit is a weak reroll target because it may leave your team after the next banner pull. Reroll on a carry that clears waves, a boss killer that stays deployed in difficult stages, a tank that keeps lanes stable, or a support unit whose effect matters in your main team. If a unit only fills a slot for one or two early Story stages, keep the shards for a permanent slot.
The stage problem decides the trait target. If the unit is your main damage unit, look for a result that raises damage, attack speed, range, crit pressure, or another direct damage condition shown by the trait menu. If the unit is a farm or economy piece, a damage trait may not fix the account's real problem; a money or placement-related trait can matter more. If the unit is a tank, survival and base-protection value can beat a small damage increase.
A workable trait is often the correct stopping point. If your carry gets a trait that improves damage or range, run that power to clear more stages before rolling for a rarer result. If your account still needs basic perks, gear, or more units, repeated rolling can hold progress inside one menu. The roll has done its job when it turns a loss into a clear, makes boss damage relevant, or lets the unit perform its assigned role.
Sub-traits need extra caution. If the reroll menu does not lock a main trait or sub-trait, a good main trait can disappear while you roll for a better sub-trait, and a good sub-trait can disappear while you roll for the main result. Combined perfect results are late-game luxury rolls. For normal progression, keep the first roll that supports the unit's role and spend the saved shards on another permanent unit.
Auto Reroll fits only after the target is strict. Before Auto Reroll starts, set the keep result and make sure the shard stack can survive a bad streak. Leaving auto rolling active while distracted can spend a shard stack quickly. If the config target is mismatched or the target is too rare for your shard stack, the account can lose a large amount of reroll currency without a stage-clear improvement.
Trait Shard farming fits a stable team. Reroll-related routes can include Raid Shop, Squadron, challenges, codes, or selling banner summons depending on the update. Those routes support a trait plan rather than every new unit. The player route is simple: identify the unit that blocks progress, roll until it gets a role-matching trait, then return to Story, raids, or material farming to test the result.