As per my other stories, Rain World is a survival game you can buy on Steam. All warnings due, because this story will have spoilers for the Saint campaign from the Rain World: Downpour DLC. With that warning out of the way, let’s get into it.
In Rain World, the Triple Affirmative is an unknown being that is spoken about by the iterators. It had started with Sliver Of Straws’ leftover data pearls and conversations between other iterators. As was stated by the others, Sliver mentions a fight for territory between slugcats, and a specific color is mentioned; green. With that, it’s easy to assume that the Saint has been around a long time without being discovered. In game, there is no other mentions of a green slugcat aside from when Saint comes into the equation. From researching the iterator logs, Sliver of Straw has been encouraging about the Triple Affirmative for awhile, long enough for most other iterators to be aware of it. There is one specific conversation between iterators though, where its existence were thought hard about. Sliver of Straw has been the only one to ever mention about the Triple Affirmative that’ll solve the immortality of Rain World‘s loops. From the Saint gameplay, you learn that they are the only truly immortal slugcat, and in their ending they become an echo, just as the ancients had. Still though, they ascend Looks To The Moon (Also referred as BSM) and Five Pebbles (also referred as EP). Upon EP and BSM being ascended, Saint travels to Rubicon and finds the two in an old Iterator Chamber, where it is revealed that Rubicon is a place after death where they are stuck for eternity, somewhat similar to purgatory. After that, the Saint will go and ascend the void worm which leads it to it’s ascension to be an Echo. The provided image is at the end of the Saint campaign, after the Saint has ascended and become an Echo, permanently trapped living.