Strength is a general stat in Xenoblade Chronicles. Generally speaking, the higher a character's strength, the more damage will be done by their auto-attacks and physical arts. Strength can be increased through skills, gems, arts buffs, and leveling up.
(Strength + Weapon Damage) = damage of auto-attack
(Strength + Weapon Damage) x (Physical Art Multiplier) = damage of that physical art
Physical arts have different multipliers which are dependent on their level. For example, Sharla's Metal Blast art at level 8 has a 2.25 multiplier and her Head Shot at level 7 has a 4.02 multiplier. This means Sharla's level 8 Metal Blast will do more than twice the damage of her auto-attack, and her level 7 Head Shot will do four times her auto-attack damage.
- Main article: Ether (Stat)
No matter how much the strength of a character increases, their ether arts will not benefit. Ether attack arts will, however, benefit from equipping a weapon with higher attack or raising the weapon's damage range with Attack Plus or Attack Stability gems. Additionally, Ether Up gems will raise a character's Ether stat, as will linking certain skills. While an Ether Up buff or Ether Down debuff is in effect, the character's Ether stat will be raised or lowered by the corresponding percentage.
- Main article: Gem
Strength and Attack Stability / Plus gems serve similar purposes, which can be difficult to differentiate for players.
Looking at the above formula to see how resulting damage of physical arts comes about will often lead players to choose how to set up their character for maximum damage with limited gems / skill coins / arts slots. It is a case by case thing, but generally speaking, by making only one change, a significant increase in damage from Attack Plus gems would be discovered, because late weapon games have such high damage ranges. But if many changes are done, choosing to use "many" buffs, auras and skill links, then strength becomes crucial; this is because there are many ways to increase strength but few ways to increase weapon damage.
Late in the game when weapons have much larger damage ranges, a single maxed out Attack Plus gem (+50% to a weapon's max damage) appears to give far more benefits than a single maxed out Strength gem (+100 strength to a character). Depending on the characters strength, adding using a maxed Strength gem will seem to give a meager ten to twenty percent increase in physical arts damage. Whereas if the same character uses a maxed out Attack Plus gem on a late weapon game (like any weapon with over 800 maximum damage range) will find over four times the increase in damage compared to the strength gem.
For example, if Sharla's gear and skills are completely unequipped, her Head Shot art will deal a maximum of 4860. Giver her a single +100 strength up gem and her Head Shot art will now deal a max of 5262, a modest increase of 400 damage. Removing the strength gem and using a +50% Attack Plus gem instead will make her Head Shot deal a max of 6569, an increase in a whopping 1709 damage with a single gem.
However, it is easier to increase strength than weapon damage. The only things that can increase weapon damage are Attack Stability / Plus gems (+50% increase in min/max range of weapon) and Reyn's Battle Character skill which increases weapon damage by 10% (to both min /max). However, for strength, there is a limit of +150 strength that can be added to a character through gems, which may seem unimpressive.
But if strength is increased through skill links and buffs, such as Riki's Nutritious skill (+50 strength) or Riki and Melia's skills that increase strength during the night (+30% total strength combined) or Dunban's Invincible Hero skill (+10% strength when HP is max) or Melia's Summon Flare arts (+20% total strength, per application) and the results can be noticed when many of them are using in combination. This is especially true for Dunban, Reyn and Fiora who have roughly 500 to 600 base strength at the end of the game when armorless. Now take it a step further. At this point with all this strength amassed, when Dunban uses his Peerless aura his strength will mercilessly be increased an additional 145% on top of everything else. When Reyn pops his Berserker Aura for an increase of 210% strength, he is capable of producing massive damage.
Unfortunately, Fiora's own arts do not increase her strength as drastically since she is a hybrid character, and does not necessarily specialize in physical / strength related areas. Of course, both strength and Attack Plus / Stability gems can be used.