Here’s a quick guide to experiencing all of the content in Slimy Sextet.
Slimy Sextet Quick Ending Guide
The gender you choose for the Slime protagonist does not change the story content in virtually any way other than changing the appearance and voice of the Slime character. You can safely choose whichever you prefer. After finishing the game, if you want to change the slime’s gender for scene replays that you’ve unlocked in the “Extras” menu, just start a new game and pick the new gender, and it will swap which gender is used in the Extras menu.
Following the gender choice, there is a large section of linear, choice-less story, until…
About mid-way through the game, you will be shown a menu that lets you choose one of the six girls in the story to view an optional scene for. Once the scene is over, you will return to the menu to view more scenes or continue on to the final section of the game.
In this section, you should view all of the girls’ optional scenes to unlock endings 2 & 3. If you skip any of them, the game will lock you into ending 1.
After this section, the game proceeds to the branching endings.
The first ending will be the only ending you can choose if you skipped any of the girls’ optional scenes, but it can still be chosen if you view them all. When the game gives a choice, just pick “I can’t fight this much power…”
When the game gives you a choice after the optional scenes, pick “I’ll resist it for my beloved broodwives!”. Then, when a second choice appears, pick “Seal myself away from the world to prevent a tragedy.”
When the game gives you a choice after the optional scenes, pick “I’ll resist it for my beloved broodwives!”. Then, when a second choice appears, pick “Believe in myself. I’ll overcome this with my love for my harem.”
Thanks to Belgerum for his great guide, all credit to his effort. you can also read the original guide from Steam Community. enjoy the game.