Battle Soul

Battle Soul (, Battle Soul) is one of 's s in Xenoblade Chronicles. It allows Shulk to sacrifice half of his current HP (rounded down) to fill a portion of his Talent Gauge.

Overview
Battle Soul is Shulk's most situational Art but is also one that can make the difference between victory and defeat. The most obvious use is to quickly gain access to Shulk's Monado Arts before a vision comes true; for example, if Shulk normally wouldn't be able to fill the Talent Gauge fast enough to activate and save the party from an enemy's Talent Art, spending half of his HP to be able to speed up the process can be a lifesaver. Battle Soul can also be used more aggressively, as losing HP while Shulk doesn't have the aggro might be completely safe—he can use it to fill the Talent Gauge, use a damage-dealing Monado Art, then use Shadow Eye to reduce any aggro that generated and/or Light Heal to get some of his HP back.

There are a few things worth noting about Battle Soul in order to get the most of it. First of all, it always costs 50% of Shulk's current HP to use, but the amount of Talent Gauge he receives in exchange increases as the player levels the Art, so while it starts out somewhat underwhelming it can be much more worthwhile after some AP investment. Secondly, because the HP cost is determined by Shulk's current HP, it effectively costs less to use the more damage he's taken; if Shulk is close to running out of HP the player has even more incentive to use it, as spending for example 25 out of 50 HP is far better than spending 1000 out of 2000 HP for the same amount of Talent Gauge, and any attack taken at 50 HP will probably be fatal either way. Third, if the player is not in direct control of Shulk it can be risky to leave Battle Soul on his Arts Palette, as the AI tends to use it somewhat more recklessly than a human would, so the player may want to temporarily remove it until they take control of Shulk again.