There's a Japanese wiki you can google translate (First result if you google "sequel awake wiki").
Anyway there's different requirements; story progress, getting affection high enough (spending time, doing talk scenes around house and the world (speech bubbles), giving gifts), getting lust high enough (gift cloudy liquid if relationship level is too low for sex toys), gifting specific items (eg Lec needs to gifted assorted sweets, then talk to her after).
Also different triggers; talk, speech bubbles, going to certain places in house (EG visiting their room, toilet). AND some of these are only available during day/night.
I honestly haven't even got all the scenes after 100% the game yet because of how ambiguous the triggers are.