It is stated in the manga that the stronger a slayer is, the more effects one can visualize from the slayer. (For example, since Rengoku is extremely strong, he produces a lot of flame effects)
I suggest implementing this into DSRPG.
There will be 3 "intensities" of visual effects:
1: Level 15- 100
Slayers still have a normal nichirin blade trail. Skills do not produce as much effects (For example, water breathing doesnt produce that much water effects), and there will be no environmental damage.
2: Level 100-170
Slayers have a slight custom trail depending on their breathing. Skills produce more effects. There is little to no environmental damage.
3: Beyond 170
Slayers have a full custom trail depending on their breathing. Skills produce a lot of effects. Skills also cause noticeable environmental damage. (For example, the ground breaks below a water user's feet when the he uses water breathing 1st skill)
Sound breathing is excluded for obvious reasons.
Breathings should still be easily distinguishable from one another, but should make the user look more powerful/weaker.