sleek current
To make it lore accurate, slayers and marked slayers could become hybrids and gain their hybrids buffs, as well as keeping their breathing style and slayer mark buffs. If a non-marked slayer becomes a hybrid, they cannot awake the mark as after(Maybe add a wip product to lose hybrid). Hybrids would have the same progression as pure demons, but they would still have to train their breathing and some of the regular slayer progression(They could also lose their nichirin blade and use different blades)
Pure Slayers would get their Slayer Mark obviously. But they could also get mastering in a second breathing, like Tanjiro did it in the show using water, sun and thunder. If breathing styles have passives, they would also get these passives and they still have to complete the breathing quest as normal. The feature of global cooldown would be essential for this to work, so people don't use braindead combinations and combos(Adding a wip product to reset secondary breathing would also be good). This would make slayers very tatical during pvp when combined with other weapons like guns and shinobi bombs.
As for Pure Demons, they could get different demons forms like in DSRPG2, but these forms are significantly stronger and put them on pair with marked slayers and hybrids. These forms would have different passives and features such as an extra arm that gives an extra m1. As well as hardened skin that reduces damage taken, or maybe wings that let you fly for a short time(These are just examples but the idea is features that hybrids and slayers can't obtain). And at higher levels they could get BDA awakenings.
This suggestion has many gaps and some things might not sound as balanced as it did for me, but it's a idea that I think if worked properly can make the combat more fun and variable.
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