I don't get why Blaze Release is an Advanced Nature.

[Shadow Phantasm]

So, now moving onto the second topic(since thanks to everyone, that was awnsered for me),

Can advanced natures originate as off-shoots of a non-nature technique, or a basic nature?

It can be both if the user of a particular nature has mastery over it.

 

[From the Dark Spire]

Sure, Steel Release does come from Earth release, and whatever else that's mixed in that makes the Earth, "Steel".

 

[Biozim]

Would you also say that Body flicker is somewhat related to Swift?