Overpriced and low-impact. It costs $4 and rarely causes more than $3 of damage. This is weak efficiency, you're paying a considerable amount of $ for something which doesn't hit much harder than Pop-Up Window and has much less long-term utility than $4 Kakugos or Border Controls. The kind interpretation of Karuna is that it's a slightly-upgraded version of Envelope, itself a $4 ice which usually causes a $2-swing (a fake Pop-Up Window).
Jinteki doesn't have a lot of cards I'd want to protect early with a Karuna, and those cards (Rashida and Regolith Mining License) usually work better early with low-cost end-the-runs like Whitespace or Vanilla. Karuna costs enough that you probably wouldn't want to rez this early on a central server unless you have some econ running by that point. Spoiler: as Jinteki you probably won't, your economy is usually the slowest and the least able to bounce back quickly from a $4 expenditure. Even Kakugo is hard to pay for sometimes and it is a Jinteki workhorse which produces considerable long-term value for a short-term tempo loss. For an extra $1, you can get a Saisentan which is devastating enough on early facechecks that you can feel fine even if it bankrupts you.
For early game chaos, I'd suggest Komainu and Saisen-tan. They're a more devastating face-check and hold up better against Boomerang and Botulism. Or, in lower-econ setups, Aiki is extremely cost-effective (but not strong enough to scare away Stargate or Diversion of Funds without help).
— superheronationI agree that Saisentan is better, but three early ICE isn't normally enough. Komainu has rotated, sadly. So Karunā is often the next-best option. (Aiki is an interesting idea, but it's a card that can easily become a liability later in the game.)
— callforjudgementAnansi means that runner don't usually facecheck Jinteki without a killer. So I think the narrow use case here is early in the game when you can't rez a spider. Would be much more playable as a code gate or barrier, but probably not thematically appropriate.
— Agasha
In my experience, Karunā is more about protecting centrals early than protecting remotes only. I agree that it's only borderline playable, though (even though I have it in one of my best decks – it's hard to find good early defence in Jinteki).
— callforjudgement