Really? How much of it did you watch? It seemed very suspicious to me. Most notable is that he very rarely uses level 2 spells, even when his gauge is full. He opts instead to perform needlessly risky dodges. On top of that there's the fact that you should be using them for scoring anyway, even if you could survive without them.
At times he seems needlessly precise with the scope, stopping directly under spirits from pretty far away and tapping shift for a fraction of a second, as opposed to sweeping sideways to ensure that he doesn't miss. Not a huge indicator, but still, it's there.
He seems to have a very good idea of where fairies and spirits are at the top of the screen, especially considering the dodging he's doing at the bottom. This is particularly true against Komachi and Eiki. A big advantage of Marisa is her laser's ability to sweep the screen without you needing to know what you're shooting at. He rarely uses it, not even to destroy boss attacks.
He never uses a level 1 to go through bullets. Not a sign of cheating by any means, but it suggests a lack of experience.
Various highly skilled dodges throughout, particularly against Eiki. One of the more suspicious ones being what seems to have been a very risky dive to catch a danmaku item (which quite literally does nothing) at the last second.
I see a lack of wall hugging against Eiki, which in general gives you an easy lane up and around the bullets.
Also note that he did not come to the board with pre-existing scores, as you might expect of one who has a long history with the game. And this isn't the first time he's been suspected of cheating.
Most of these's aren't truly sings of cheating on their own, but they are signs that player is not very familiar with (good at) the game. If he's not a cheater, than he is someone who picked up a game of which he has a very limited understanding and brute forced his way through with sheer dodging ability, and all the while displaying an insane degree of confidence, taking completely unnecessary risks.
I'd like to hear as many opinions on this as possible, but as it is I'm quite convinced.
I refuse to believe any kind of slowdown tools were used here unless the player was actively trying to conceal it by reducing the amount of actions.
I think it's safe to say that, if he was cheating at all, he was definitely trying to conceal it.
