PiBiAo

 is the poly ship between Aoba, Bill and Pina from the Beastars fandom.

Murder Incident Solution arc
Before meeting Pina, Aoba and Bill were the closest of the trio. They were always seen being together during club activities and they both seem to know each other well. Aoba appreciates Bill's social abilities, considering them as his "specialty", both used to share the ideology of eating meat to reach maturity, but when He had the opportunity to eat meat, Bill continued while Aoba fled, because of this, Aoba came to discriminate against Bill for eating meat, but seeing that Bill was not happy with his decision, he became more empathetic with him. Bill also admires Aoba, as he himself talked about how righteous he is.

Pina suddenly makes his appearance entering the drama club's male dressing room where he interrupted a heated argument between Legoshi and Bill. Pina occupies the locker that used to belong to Tem. He highlights the scratches on Legoshi's forearm and casually asks him how many stitches did he need. After leaving his things Pina says goodbye telling them that they can fight to their hearts' content, and he leaves without even giving his name. Legoshi and Bill stop fighting, as Bill diverted his anger to Pina's obnoxious attitude, asking if Pina was a new member, addressing him as "that pretty boy". Aoba answers him by saying Pina didn't introduce himself and commenting about how he called Legosi a "doggie".

Shortly after, Pina appears before the members of the club, revealing that he joined the club because they asked him, but he doesn't know much about how the club works, and amiably says that hopefully everyone can have fun and get along. Bill interrupts saying if perhaps they plan to make Pina Louis's replacement. Pina asks if it is a matter of appearance, stating that students like the drama club but it's tough without the star actor Louis. Pina remarks that the drama club would have a hard time without a distinguished and handsome male actor, and alleges how carnivores' eyes lose their shine from being consumed by their desires and instincts and that these are just not beautiful. This comment offends all the carnivores in the club who interpret that he is calling them ugly, including Bill and Aoba, who are carnivores as well. Pina states that his only redeeming trait is his looks as he doesn't have "herbivore pride" or a conviction.

Some time later, Pina gets the starring role in the New Year's school play and happily mentions that he will be the handsome young man whose soul will be stolen by a reaper and will die at the end of the story. At the drama club, rehearsals for the school play begin and Juno tells Pina that he doesn't look so good and asks if he remembers his lines. Pina claims that he remembers them. So they start practicing their lines, where Juno gives rise to Pina's dialogue and after pausing, he recites his lines emptily and in an impulse of emotions with all his energy Pina finishes reciting his lines, leaving all the club members stunned. Sanu orders a break and Pina walks past Riz and asks if he "saw that", leaving the shocked drama club members behind. Including Bill, who once again mentions Pina's beauty, thinking about how aside from being good looking, he is also good at acting.

Revenge of the Love Failure arc
Several months later, Pina interrupts Bill when he is about to eat a newborn chick that had hatched from a shocked egg. He highlights that this is the first time he had seen a shock egg and asks Bill if he will eat it. Bill, alarmed, asks him what he is doing in the carnivore dorm kitchen, and Pina answers that since the herbivore dorm kitchen was full, he came to this one. Pina tells Bill that if he wants to eat the chick in the soba, he will stand there and watch, and maybe he will learn something. Pina makes a comparison with Bill and Riz, saying that Riz is now in juvie for eating a classmate and Bill can now eat a baby but can carry on living a peaceful school life, claiming that the world is unfair. So Bill yells at him telling him that he is not going to eat it, so Pina proposes to save him. Although Bill claims it is too late for that, Pina declares that they should try. After putting the chick in a thermos in the drama club warehouse, unable to get help from the infirmary and see that the chick is not improving, they have the idea to enlist Aoba's help, whose warmth and presence seem to keep the chick in good spirits. Pina asks Bill if it is not great that now they have the opportunity to save the chick. And while the three of them cuddle, with the little chick between them, Bill asks if the anxiety he is feeling is some kind of anxiety that males have when they start a new family, implying the chick he found could be the child to the little family the three of them started.

After taking care of him for a week, once he is healthy enough to go outside, the trio take the chick to a police station where they give him to an officer, and say goodbye. Pina questions Bill's intention to remember the chick's face claiming that he will not recognize him anyway once it turns into a chicken. Bill alleges that that is not the issue. Aoba advises that Bill should stop going to the Black Market for now, so Bill states that he will never eat chicken meat, because it would be terrible if the chick ended up in the Black Market, although he does not say that he will stop going. Pina proposes to go eat soba for lunch but Bill alleges that he will never eat soba either.

After several months, Bill is reunited with Legoshi after he temporarily returned to Cherryton to take refuge. Legosi compliments him saying he is actually a good chief, to what Bill replies, a bit flustered, and looking at where Pina is sitting, that he is doing all of that work becuase he loves the drama club's herbivores with all his heart and soul. Although he says he keeps that a secret.

The last time we see the trio in the manga is in the epilogue of the story, after the Cherryton Academy returned to the interspecies education system thanks to Louis' press conference. Pina happily declares that he will miss Bill and the others when they graduate (which will be in a short time), but annoyed Bill tells him that Pina can fool girls, but not him. Next to him, Aoba smiles contently.

Quotes
"Who was that pretty boy?! Is he a new member?!"

- Bill, referring to Pina, asking Aoba about him, Chapter 58

"He's good looking AND good at acting...?"

- Bill, thinking about Pina, Chapter 87

"I'm not righteous like Aoba, or attractive like Pina..."

- Bill, thinking about Aoba and Pina, Chapter 155

"I'm doing this because I love the drama club's herbivores with all my heart and soul, though that's a secret."

- Bill talkig while looking at Pina, Chapter 152

"Is this some kind of anxiety that males have when they start a new family?"

- Bill asking Pina and Aoba this, referring to their newly found family, with a little chick as their child, Chapter 155

"I'm gonna miss Bill and the other senpai when you guys graduate."

- Pina, Chapter 196

Fanon
is a rare poly ship within the Beastars fandom. So far it doesn't even have fanfictions on AO3. It's overshadowed by more popular ships, specially with Pina, such as PinaxRiz. Most PinaxBilxAoba fans started shipping the trio due to the entire chapter 155 being dedicated to the slice-of-life story of how they made a family for that little chick they found almost dying out. The trio is adorably called "gay dads" and "the cutest family" by some fans of the ship.

Fandom
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