I've dealt with this technique question before. It's actually a common misconception since there isn't any "night blossom" skill in the game. For stealth assassinations, you'll want to focus on the tools mastery tree, unlocked through knowledge points from shrine challenges and contracts.

The best approach is maxing out your kunai skills first, then getting smoke bomb upgrades which really opens up your stealth options. During night missions, stick to the shadows and use shoji screens for cover, and remember that timing your strikes with environmental distractions works great. Getting those mastery points might take some grinding but focusing on side activities, especially the shrine stuff, speeds things up quite a bit.

A neat thing to know, seasonal effects and time of day actually influence your stealth effectiveness so plan your assassinations accordingly. Stack your tools right and you can basically chain takedowns without any special techniques, just need proper positioning and timing