Well, if someone actually let him get it to that point, it might as well be immovable, card effects or no card effects. It'll kill you as soon as it gets an attack in unless you've taken little to no hero damage.
but that can happen in any card-game Does Shadow Era has counters to those attachments though?
It does. Well, while it's at this particular point, the opponent would've already been dead many times over, as I've ignored attacking for a few rounds just to see how high up I could actually get. None of the usual "Send ally away" cards such as
Retreat! or
Dagger of Unmaking would work as he has Steadfast (he cannot leave play unless killed).
But should it actually happen in a live game, any of the following cards would be valid counters:
Sever Ties: To remove any of the attachements he has. It's not a direct counter, but can mitigate the issue to some extent.
Logan Stonebreaker: Could use his ability and simply hit Kairos in the face. If he deals any damage, Kairos dies, thus bypassing Steadfast.
Death Trap: Can be used to counter him from getting on the board at all. Takes some luck though.
Tidal Wave: Gives absolutely no shits about what you build on Kairos. It kills everything, unless protected from damage (such as a stolen
Holy Shield or similar).
Mind Control: Direct counter, AND it will hurt me a lot in the process.
Black Garb: Is a very cheap counter and can be used to bait out Kairos. However, if he's that high of damage, it may not be worth it, as you have to be hit for the garb to trigger and it will only reduce damage taken by 2.
Crescendo: Will absolutely kill him, but it's gimmicky and requires me to be out of high cost item removal for it to work. Kairos can still kill you within those five turns as well, unless you have stalling cards.
Magma Jackal: If you get this out and it survives its exhausted play turn, it will easily deal with Kairos as he will be killed by the passive. Naturally, I would not attack this with Kairos as it would lead to his doom. But if I can't disable or kill it in any other way, it will run face first into Kairos, killing itself.
Tiger Wulf: A very nasty card that if allowed to live its exhausted turn will easily deal with Kairos.
Dragon's Tooth: Since Kairos is a 6 cost card, he will be killed by this.
Voracious Arachnid: I'm only adding this for completeness sake. You'd have to get it's attack over 6 for it to work, and that's a lot of buffing. A sensible player would have killed the arachnid far before that happens, provided Kairos was already on the board.
The Bigger They Are: The go-to fatty killer. Play a cheap minion, then play this. Boom, dead Kairos.
The Harder They Fall: Its companion. Also works.
Crippling Blow: It's technically a counter, but as I'm playing him with
Super Focus, it's a moot point as he'll be immune to enemy attachements.
So yes, there are plenty of counters. Which is why I claimed that if this is allowed to happen, you deserve to be hit by Kairos in the face ^^