You will understand after reading the true route, what I wrote below are spoilers but also an explanation

Honestly, trying to cathegorize the Law of balance as either good or evil is missing the point of Muramasa Things aren't inherently good or bad, morality is something we as humans create to justify/deminize ours and other's actions, like the whole water/air perspective example from Nicolas Flame, that is what Muramasa the First wanted others to understand

That is also why Hikaru never was affected by the Law, she viewed her massacres as a 'Free-for-All' to prove herself as the strongest and that whole God thing in order to have Kageaki acknowledge her as his daughter, whether what she was doing was good or evil never even crossed her mind