Completed all storylines of the characters up to this point.
Defeated all bosses, including secret ones and blades. Only 2-3 story bosses remain to be defeated.
Collected all weapons, armor, seals and spells that can only be collected during the first playthrough. I could have missed something from consumables, but there are materials for pumping.
Saving was specially made at this point so that you can easily get to the secret ending.
How to get to the secret ending:

Talk to Shirley in the location "Hagios Patir - Path of Perfection".
She will ask you to get rid of the toy bunny. We go to the abyss and press the action button.
Talk to Shirley again.
Move to "Sunset Hill - Arboretum".
Talk to Delfa. He gives us an item.
Return to Shirley and give her the item.
We continue the game, defeat Loskid, the father, and the secret boss.
Enjoy the secret ending.

Installation instructions

Download the file
Unzip with replacement of files along the path C:\Users\user\AppData\LocalLow\SenseGames\AILIMIT
Launch the game and click "continue"
Perhaps it is worth making a backup of your own saves

Author: Vledushok