Quick ability breakdown: Dragon slash is a quick dash-slash, able to get you out of corners and bad positions. Dragon slayer covers the whole screen (without gear) and can cover more than what you see (with tactical visor). This can quickly kill the mini-bosses (gunner, tank, and cyber ninja).

Maximizing the abilities: For dragon slash, try to only use it when there's a line of 4 or more enemies but be careful that you don't finish your dragon slash right in front of an enemy (enemies swing their sword whenever they notice you in front of their target zone so they can catch you in the short end animation of dragon slash if you end RIGHT in front of them).

For dragon slayer, your only worry is the spawn rate of the enemies (the following numbers are my experience with spawn rates using the tactical visor). If your screen is full of enemies, the average count seems to be around 10-16 enemies (other than the first 100 kills due to the spawn rate being so slow that you might only get 8-13 enemies). *If you are using dragon slayer at the end of a hundred, be careful about using it too early. If you're too early, some enemies might not have spawned in yet and force you to wait as they walk out of their spawn and enter your screen (if you practice enough, you can remember where exactly the spawn locations are and pre-fire with your gun to hope and hit them off-screen).

Some of the numbers in my dragon slayer paragraph may be a bit off but these are the numbers I recall (it's been about 2 weeks since I've ran Akane speedruns)