Hiya Lucy!  Getting the Perma Ending is a teeny bit complicated, but I'd be happy to break it down for you.

First, you need to start Week 9 with your PR lower than the PR Goal for your selected difficulty.  This is easiest to achieve by setting the difficulty to Hidarugami and/or spamming Put Over every week to ensure your PR gains are as small as possible.

If you're on track to fail meeting your PR Goal, Charlie will approach you just before your Week 9 Match and talk about what would happen if 'hypothetically' the CAR was disabled and you failed to reform.  You will be given a dialogue choice.  Say, "I'd rather have that happen to me than leaving MAW."

Once you've made it clear to Charlie that you are on board for getting perma'd, the final step is losing your Week 9 Match.  Again, spamming Put Over will guarantee this if you're worried you're going to win by accident.  If you got the correct Charlie dialogue prior and picked the correct dialogue choice, losing your Week 9 match will get you permanently digested.  The details of your ending can vary depending on which opponent digested you, the method they used to vore you for the last time and the content filters you have in place.

I'm not positive what you mean by 'anything else', but I assume you mean how to get the other endings?

The Good Ending is achieved by getting high enough PR to reach your difficulty's goal.  Simple as that.  If you beat the game on Ravenous or higher, you will also unlock a secret fourth class.

The 'Retirement' Ending is achieved by failing to meet your PR goal by the end of the Week 9 Match, without taking the steps required for the Perma Ending.  Either tell Charlie you don't see any appeal in being permanently digested, or win your Week 9 Match.

Hope this helps, and thank you for your interest in my game.