How to pass the Cerberus part? the fight got 10 min long, had more than 1000 essence and It didn't ended

hey. so im stuck now at what i assume the end of the game. i unlocked almost the whole gallery (only one left, which i didn't encounter yet)

so last thing i did was unlock the giant golden door and i chose to lunge at kaatriv and then the credits rolled. i closed the game and launched it again without saving thinking i wanna see what happens if i lunge at other girls. 

after launching again when i go to the golden door nothing happens, no dialogue no nothing. but i unlocked the forest.

so i enter and fight in the forest. and collect what looks like lewd flowers, they have the mission star on them. but i keep collecting them over and over i dont know what should i do with them or where to use them. so that's where im stuck idk how to progress from there. 

thanks.

I continue attack the boss (more than 5 min) but cant defeat them. Is that a bug? 3.0.2