@NL
sorry to take it a bit personally, because i was among the 5 -only- posters before your post.
I remembered having seen OP's video before so i knew his level. OP may not know me, I think i'm not too far from his level, and my hitting partners every session are definitely as strong or stronger than both OP and that girl.
Its even more apparent on the points highlighted by zeio , especially the 2nd one [watch his right leg], but OP is going back and upper body going up while hitting the ball. Whether a kill shot or even a simpler receive, its not a good thing to do, and that needs to be corrected. He can just think about it, or perhaps he's doing that because he's surprised a bit so because the girl is good at long serves, just going back 5-10 cms in the receive position will give him the extra 1/10th to react.
OP has not made a single post since. I'm curious to know why he wants to kill the ball receiving ? is that his real intention ? he's good at rallies, and on the 1st point shown by zeio, even if it wasn't the best of all possible receives, it was good enough to force an error. If he wants to play a stronger BH when receiving, first don't go back, then its not about making a big stroke or using a lot of power, because the incoming ball is fast its really about timing taking the ball earlier I think and having the perfect angle (usually more closed than usual) adapted to the incoming spin. Be relaxed and use more wrist, and have a shorter stroke.