Asahi Lina has the same spanish-sounding accent as Hector but pitched up and falsetto. "raider" - the hostname of the developer machine is that same as the hostname of Hector's machine.
That looks pre-recorded, and the second person talking with Lina is clearly following a script, I don't think they could do it that well on one sitting, and the animations are probably not automatic.
Probably some pre-recorded, agreed upon advertisement to promote a new channel.
Well then it must be legit. Who among us hasn't accidentally leaked a cryptographic secret key to a screeching vtuber who has the exact same accent as we do.
Even if you had the stream key¹, I wouldn’t expect you to be able to take over a stream with that kind of clean cutting from marcan to loading throbber to Asahi Lina. Without any knowledge of what YouTube Live actually does about conflicting input streams, I would expect the takeover to (a) be instant, (b) fail, or (c) produce a garbled mess. What the thirteen second throbber delay would be adequate for is starting up whatever software you need to play the part of Asahi Lina.
I have no specific knowledge, but it seems very clear to me that at the very least marcan is a collaborator in the persona of Asahi Lina; and absent further contrary evidence, them being the same makes sense.
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¹ And if stream key exfiltration actually happened, I find it hard to imagine anything but acrimony arising.
He even did a super-cringe "take over" video, where Asahi Lina "broke into" one of streams: https://www.youtube.com/watch?v=effHrj0qmwk