Here you can find links to all of the walkthroughs for Nightshade / 百花百狼 (also known as Hyakka Hyakurou ~Sengoku Ninpouchou~).
Every route is available from the beginning of the game (no need to unlock anything), but some routes are a bit more spoiler-heavy than others.
My recommended play order is as follows:
Goemon → Hanzō → Chōjirō → Kuroyuki → Gekkamaru
Banner image: Nightshade / 百花百狼 (Hyakka Hyakurou ~Sengoku Ninpouchou~) | Red Entertainment & D3 Publisher