I think this would probably be better named as "The Power of Kindness"
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The problem with this suggestion is it would make the title too vague and too easily confused with something very different that is probably if not definitely covered under other tropes; "The Power of Kindness" could just as easily be "you did something nice for someone and it made a big impact" - which could include mundane acts, and is something that could be covered under say, The Power of Friendship or The Power of Trust or even The Power of Love depending on circumstances.
THIS trope on the other hand, is very clearly about an actual supernatural/paranormal ability being used to bolster heroes and/or destroy or force a Heel–Face Turn in enemies.
A perfect example (which is already on the list under Comic Books) is the Blue Lanterns from DC: their Hope/faith-based superpowers allow them to physically heal pretty much anybody, and purify away negative emotions such as fear, greed or even the enraged hatred that drives the corrupted Red Lantern Corps members - this Blue Lantern power, the same that can heal bodies, severs the connection the Red Lanterns' Power Rings have to them, returning them to full control of themselves when they previously had been under a More than Mind Control situation with their anger being deliberately and perpetually aggravated. That's not just the Power of Kindness; in the case of a Red Lantern, the Blue Lantern is simultaneously using a pseudo-mystical power to forcefully drive out the victim's paranormally-aggravated Rage, break the psychic and physical connection they have with a piece of Sufficiently Advanced Technology in the process, AND physically healing the damage that the Red Lantern Power Rings do to their hosts (whose bodies are so damaged by what the Ring does to them that they can no longer survive without it unless someone with super duper borderline godlike healing powers intervenes).
It's the difference in other words, between Sailor Moon offering to forgive a villain...and her using her magical "healing" powers to purify the Monster of the Day into dust. Big, BIG difference, especially as Kindness can't generally physically hurt a person, whereas this CAN if the recipient is truly evil/corrupted in specific ways. Another example being some versions of D&D, where Radiant type powers can do extra damage to Undead creatures, right up to and including the possibility that a spell meant to heal, can do actual damage instead if it's aimed at Undead creatures.
In fact, in that sense, it doesn't even need to originate in genuine "kindness" - a Cleric or Paladin in D&D universes knows exactly what a Radiant spell does to zombies, which is why they're using it in the first place. ;)
I'm a little confused as to whether this HAS to a beam-like attack or directly propagated by a single individual, or whether something I was reminded of while reading this would be counted. Because clearly the Indigo Tribe and Blue Lanterns count, but...well, it's best if I describe it, yes? I was tempted to add the Star Sapphires to the list of examples under the Green Lantern franchise in Comic Book examples because of this:
For some time the Star Sapphires were capturing enemies from the Sinestro Corps (who are basically an intergalactic terrorist group), trapping them in crystal structures so they couldn't escape, and then flooding them with exposure to the "Violet Light of Love". As the only example where it works is Fatality, who then breaks out of her crystal as a fully-converted Star Sapphire herself, it can seem an awful lot like straightforward brainwashing. Reportedly though, this was meant to bring out the Love already in their hearts, which may be why it only seems to have fully worked once. Most Sinestro Corps members are recruited purely for their ability to terrify others, so many of them are not exactly "loving" people. The only other case where it almost worked (before the process was interrupted) was on Cryb, a baby-stealing Sinestro Corps villain who apparently did genuinely care in some warped sort of way about the large number of infants she had stolen, as while she had killed their parents, up until she was captured she was still feeding and even "protecting" the infants. When we see the Violet Light working away at her, she's shown thinking about them and about how they're going hungry without her, and starts shedding actual tears, indicating that the Violet Light is stimulating the parts of her that feel guilt or care for others, much like the Indigo Tribe does to its own converts.
Just curious if that would qualify under this trope due to the use of the paranormal "Violet Light of Love" or if the fact that it's shown as a longer process while they're trapped in crystals (where the Star Sapphires wander off and let the power of the Star Sapphire Gem do its work) makes it a somewhat related but separate trope. It does strike me as More than Mind Control but then so does what the Indigo Tribe does and that is an obvious example in line with a lot of the others on the page, so that doesn't automatically rule out it being a bit of both.