I was expecting some half baked theory but damned if that doesn't make a whole hell of a lot of good sense.

It (slightly) annoys me that I put essentially this theory on TVTropes' Touhou Wild Mass Guessing page, with much the same reasoning, about three days before reading this far in the comic. I thought I was being original.

(Oh well. It's put much better here.)

I've always personally thought of Yuuka as a sidhe. Zun has a habit of pulling out startlingly obscure mythological creatures so I'm not sure whether it was intentional.

...This just got a lot more deep.

One niggle: Yuuka is a very long-lived youkai. You'd think if Cirno went the way of Yuuka, she'd be around long enough for the next Hieda descendents to interact with her. So how come Akyuu's freaking out?

Because it's possible that Yuuka is planning on killing Cirno if she does ends becoming a youkai.

HT_Rock said:

One niggle: Yuuka is a very long-lived youkai. You'd think if Cirno went the way of Yuuka, she'd be around long enough for the next Hieda descendents to interact with her. So how come Akyuu's freaking out?

Because just like Yuuka changed, she's afraid Cirno won't be Cirno anymore.

Andy00 said:

Because just like Yuuka changed, she's afraid Cirno won't be Cirno anymore.

Isn't that kind of selfish though? Cirno is already on her way of becoming something else than a fairy. If she changes then that is the natural course of her evolution.

If you had godly power you wouldn't suddenly prevent your child from growing up would you? That would simply be the highest level of selfishness and honestly cruel.

This is why, even if Yuuka is aiming to accelerate this shift, I do feel that such an action is far less malicious than trying to prevent change just to satisfy your own personal feelings. Sure, stop her if she is being cruel or doing it in an unnatural manner, but by all means. Cirno, who is aiming to become stronger, should be allowed to reach "Maturity" so to speak.

I feel like Hieda is being like an old gran that is panicking over the fact that her grandchildren will eventually die from age as well. A change is inevitable. Rather than try to prevent it, try to support it in a manner that leads to the least amount of damage to the person in question.