User blog comment:TAGDavid/Buddyfight Therapy/@comment-25600444-20150720172525/@comment-5777478-20150720200309

Even if the rule said to start with 6, sending 2 back would be cheating. You'd get to choose what cards to keep. To be fair, the player would have to send all 6 back, shuffle, and draw 4. BTW, that's what happended in the anime. He (or rather the deck core system) didn't send 2 back, but instead did a complete redraw.