I dont think its that hard... A little playing around with the mouse gives you left click to hit, right click to jump. Then some thinking about how volleyball is played, and timing the hit button when the ball is in range, and pointing the cursor when the ball is in your court or theirs.
I replayed it, and managed to clear it. Its just timing and luck...
Dint understand the Jap 6 years back, and still can't understand now ^^.
Edit:
Well, here are the last bosses for the volleyball game...
and here is the end...
Its all in the timing, really. And boy was Yuuko pissed at the 1st prize... lol.
Couple of hints. Don't ever choose people who are weak in sports... Miki can't even jump to clear the net. Use Meiya, Inchou, Akane, or Kei. Reserve Haruko for the last two games. There are 4 games in total.