Way of the Aether Monk?

Hey guys, so I've been lookin' at the griffon's saddlebag, and I really like the way of the Aether monk. specifically the Spirit strike ability. they can shoot a 30 foot range projectile that deals martial artss damage and uses wisdom to hit. It says whenever I could make an unarmed strike, I could do this instead. It's kinda just a better version of radiant sun bolt. the biggest thing I wanted to ask: it's counted as a melee spell attack, and as mentioned, I can do it whenever I would've done an unarmed strike. So does that mean an Echo knight could have their echo use it? and to get crazy, does that mean by RAW that that is part of my opportunity attack range??

Since Way of the Aether and Echo Knight are both unofficial subclasses from different third-party sources, there's no answer to how they are intended to work together (because they're not). But the Manifest Echo feature says that any attack you make with the Attack action on your turn can originate in the Echo's space, so if you're doing this Spirit Strike thing as part of the Attack action on your turn, then you can do it from the Echo's space. If it requires some other type of action to use, or you're using it on someone else's turn, then you can't.

Opportunity Attacks can be Unarmed Strikes, so if you can do this Spirit Strike as an Unarmed Strike, then technically you can do it as an Opportunity Attack. Technically, though, you'd only be able to do so when someone leaves the reach you have with Spirit Strike, which sounds like it's 30 feet — not a great option for an Opportunity Attack in most cases.