Chi

Chi is discussed in Basic Set as an advantage origin.
In GURPS Powers it was explored as a source for powers, which determined the value of the Power Modifier.
==countermeasures==
This is a confusing issue since the source/modifier pricing does not include a -5% for countermeasures (Anti-Powers per P20) as others like magic/psi/super do
P21 even elaborates on this under No Countermeasures:
:traditionally impossible to neutralize chi
It mentions "can use their powers to block one another" (which probably refers to a Power Parry) but:
:"neither warrior can deprive the other of all of his abilities in an instant"
Instead the value comes entirely from Required Disadvantages (P21) as specified on P26: either a Discipline of Faith or a Vow
P97 appears to imply that such countermeasures could exist though:
:Neutralize and Static should affect these capabilities
This follows explanation of both chi skills and magic skills.
GMs could be free to assume there is a -5% built into the SKILLS in which case neutralize/static would ONLY work against them, unless -5% was added to the power modifier.
==Irritating Conditions==
Chi functions in a unique way compared to how "Required Disadvantage" normally would.
Required Behavior and Power Modifier (P23) assigns:
*power vanishing speed: "Quickly enough to endanger the user in combat: +0%."
*"Add -5% if the power doesn’t just vanish but turns against the user!"
The 0% for chi is phrased like this:
:"your power fails you the first time you call upon it under stress"
The 'under stress' caveat means it won't fail when used in non-stressful situations, which is not how Required Disadvantage normally works.
This is a relative benefit, but that can be enforcing another subtle difference in mechanics:
*"Until you do, you feel ill"
Feeling ill is MANDATORY when a power fails under stress. Rather than OPTIONAL as how the basic function appears where the "Act necessary to restore" is:
*"minor harm (1d injury or an irritating affliction): +0%"
Normally you could choose to not harm yourself, or not suffer an irritating condition. You wouldn't get the advantage back, but you could choose when to time those drawbacks for when it's convenient for you.
P23 does not specify the duration of the irritating condition. 
Chi doesn't give that option to delay the irritation: it happens automatically, and lasts indefinitely until the 1d days of meditating to rebalance.
1d injury takes 1d days (avg 3.5) to recover assuming HT rolls are passed for healing. Since HT 10 only passes half the time, that's actually an average of 7 days for the average human. Martial arts masters probably have higher HT to lessen that though.
*this makes it comparable to the "week of adventuring" or "week's income" alternatives on that tier
In the interest of equivalency, the "1d days to rebalance" might be seen as "days of successful meditation". B207 defaults this to Will-6 but unlike HT it is cheaper to train up (buying up the skill or buying up will) so eventually could be easier to pass.
*unlike HT which is all-or-nothing this might perhaps use the Long Tasks rules.
==Martial==
Chi also explored in GURPS Martial Arts for special skills that use it.
==resisting==
one downside is enemies targeted with chi powers can substitute Body Control for HT rolls against them
==Quotes==
20 May 2008 by transmetahuman http://forums.sjgames.com/showpost.php?p=598574&postcount=3
:Someone with Neutralize (chi) can make you lose them temporarily, and if they have Power Theft they can actually get your skills from you. Though come to think of it, the chi power modifier doesn't include the -5% for being vulnerable to Static/Neutralize anyway, so those skills wouldn't be either.
Category:Power Modifiers
Category:Limitations