I don't know if this has been posted yet, but it is a neat trick. You have to understand Japanese; You have to watch it till the end.
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That's a great trick... although, just after Yuko places her card back in the pack, he palms the card away... in other words, the card is not in the pack any more, but somewhere on his person... . He then turns to the chap of the right, and says something, and when he turns back around, you can see that he reaches round behind the girl with his right hand, almost certainly giving the card with 'Yuko' written on to someone else... after that, the film is sped up, creating the illusion that not much time passes, when infact it was probably at least a full minute - plenty time to arrange for the next part of the illusion...
As for the card appearing 'inside' the fish tank, that's possible by sticking the card onto a thin layer of clear film/glass and sliding it very quickly into place from the bottom up.... in order to mask this, he throws the packs of cards over a period of around 2 seconds, to obscure the card being brought into place.... notice how the cards he throws at the fish tank land next to the glass... there is clearly a gap between the glass and the black support (one or two cards almost fall down the gap)... strange there should be a gap... clearly, the fish tank isn't just resting on a solid support, but the glass goes down further than the black outer support would have you believe... in this case, it's very conceivable that an extra glass layer is lurking underneath, with the previously handed-off card now stuck to it's inside face... this layer could easily be between two other layers... the outer layer (the fish tank wall) and an equally movable inner layer (which is removed prior to the part where he peels the card off the inside of the tank)... either way, nobody would notice the movement of a clear glass slide unless they were looking very closely...
(I wouldn't say for definite, but it certainly looks like the tank is atleast double-walled on the front side... looking at the corner of the tank on the right hand side of this screen-capture... )

Here's a little more proof that there is more than one glass layer on the 'front' of the tank... watch as he reaches for the card and the camera shoots from the back... you can clearly see the reflection of the card in another layer of glass... as the camera pans round to the front of the tank (the red side of the card), the reflection is no longer visible.... (since the card is on the inside layer of glass)

As for the part where he puts his hand into the tank,
that was magic
