Warning: Major spoilers for season 3 of 13 Reasons Why ahead. You've been warned.
With Hannah Baker (Katherine Langford) no longer a part of 13 Reasons Why, someone had to take over the voiceover of Netflix's teen drama. The person filling that slot in season 3 is Ani (Grace Saif), a new student whose mother is a nurse for the Walker family — as in, Bryce Walker's (Justin Prentice) family.
Throughout much of season 3 of 13 Reasons Why, who Ani is speaking to is a mystery, but when the person is revealed, so is Ani's real place within this series.
Throughout the season, Ani sits in a grey room talking with who we eventually learn is Deputy Standall (Mark Pellegrino), father of Alex (Miles Heizer) and the person in charge of solving Bryce's murder. Deputy Standall brings Ani in because of her close connection to Bryce: Not only did she live in Bryce's house, but she carried on a secret affair with him for weeks before his murder. When Ani learns who really killed Bryce, she realizes that she must spill all her friends at Liberty High's secrets in order to protect the culprits.
How Ani knows all the secrets of the Liberty High students — despite having just arrived months earlier — is more or less because Ani is nosey as hell. She and Clay (Dylan Minnette) investigate Bryce's murder together, but it's Ani who is a keen observer of the students around her and isn't clouded by her past relationships with them. Ani knows all the characters' motivations for possibly killing Bryce, but she also knows their alibis and why they wouldn't have gone through with the murder. That's how she realizes that Jessica (Alisha Boe) was there the night that Bryce died.
The purpose of talking to Deputy Standall is not just to reveal everything she knows, but to give him a good alternate suspect for Bryce's murder. Instead of telling Standall that it was Jessica and Alex (Miles Heizer) who led Bryce to his death, she suggests to Standall that Monty (Timothy Granaderos) would make a more fitting suspect. He doesn't have a concrete alibi that anyone knows of (he was hooking up with Winston, something he'd never admit) and is already in jail for sexual assault. Standall knows it's not true — he suspects his son had something to do with the murder — but ultimately chooses to go with Ani's story in order to protect Alex and Jessica.
Ani isn't the most reliable narrator: She lies and claims she doesn't know things when she definitely does. However, her narration allowed fans to get a full scope of where everyone was this year, from the murder suspects to the murder victim. Without Ani leading the way, there may be some "reasons why" we never quite sorted out.