In order to gain strength, Patchouli triggered a disaster, and many people's bodies were swapped. We need to defeat her and prevent the disaster.

I recommend using the keyboard and mouse operation mode, as it allows you to shoot while moving. Shoot with the left mouse button, activate the shield with the right mouse button, switch roles with the mouse scroll wheel, confirm with Z, and return with X. Activating the shield will consume 100 power points.Power is related to your bullet damage, and if your power reaches 400, the bullet is very powerful. So try not to use shields as much as possible. In story mode difficulty, you can use healing items without using shields at all.
There are many attack modes for bosses, and after one attack mode ends, you will regain full health.

1.At the end of the first level, do not immediately move on to the next level. Going back, you can find Marisa in the bottom right corner of the map. She has faster movement speed and more concentrated bullets, much stronger than Reimu, but slightly less health.
2.After the second level (lake) ends, return to the left side of the initial location to obtain a blue key. Get the yellow key from a hidden room in the upper right corner of the fourth level (library). You can find the red key in the fifth level (main hall). After collecting three keys, you can enter the EX hidden level in the sixth level (Time Tower).