For the first turn, be careful not to move within the range of the fairies closest to Reimu.
This is an introductory stage, so it's not that hard. Thus, when you can you should close in to attack aggresively.
If you move to the pond behind the shrine, Reimu will talk about Genji. However, this makes the WP Bonus condition hard to accomplish.
In the third turn, Keine will join your side. She's a tank-like character, so don't be afraid to shove her inside the Fairy group. Even if she does lose HP, her Trust Seishin can recover it quickly.
However, Reimu's much more weak to attacks. Thus, it's a good idea to save often in the middle of battle.
If the WP Bonus seems difficult to get on Lunatic, don't be afraid to give up. Lunatic is very harsh on these.