This achievement is story-related and can't be missed.It will unlock after beating Stage 5 on normal or casual mode on your first playthrough.
This boss fight is a little tricky due to the rain and wind. As a general rule, I advise to stay as much in the left side of the screen as possible.
When boss is flying above you, they'll make fast movements side to side. It is possible to hit them with a strike after jumping or using special attacks such as the whip (Zangetsu) or the daggers (Miriam).
Before landing, boss will make electrified spikes fall on the floor. Dodge them and hit the spikes to clear space and try to reach boss's position so you can strike them a couple more times.
There are two things to be careful with:
- If boss lands on your left, crouch to avoid his blast, otherwise it will push you out of the plataform and you die;
- After receiving the last strike, boss will position on top of the center post. A few seconds later, he'll bring some vertical lightnings on both sides of the screen. As soon as this happens, try to stay as much closer to one of these lightnings as you can, without touching them of couse.
Please refer to this video by YouTube user DenSetsu for the complete fight: