Use your mouse and keyboard. Position the crosshair and click on a Fairy or Hong Meiling to throw a knife. The light around the crosshair is the hitbox for incoming bullets. You can also shoot down bullets by clicking on them as well. Shooting knives deplete the knife gauge. If the gauge is getting empty, wait until it replenishes.
Hold the 'Z' key to freeze time. You can fire knives while time is frozen and avoid possible bullet hit. However, the large gauge limits on what you do. Release 'Z' to unfreeze. Replenish the gauge by shooting down fairies.
When Hong Meiling appears, she attacks with various spell cards and is time limited. Try to throw knives at her. If time expires or the enemy life gauge is depleted, she disappears, waiting for a while before reappearing with another spell card.
Sakuya Izayoi has three life points. When an enemy bullet hits the light area, she loses one life point. The game is over when all three life points are lost.