Project Silent Sparrow

Project Silent Sparrow is the name of a portal that was built by Krei Tech as Alistair Krei tried to make science fiction a reality on Akuma Island. Yokai used the portal as a weapon agents Alistair, so he can complete and get his revenge.

Lore
Hiro Hamada saw Yokai bringing one of the three parts of the portal to San Fransokyo Bay, but had no idea what it was, for or what the red bird logo meant. After upgrading himself, his friends and Baymax, the team headed to Akuma Island and discovered the last part of it as they were trying to find Yokai. The team watched footage from the control pit and saw Alistair Krei demonstrating the portal to the garment.

There were two portals and as something went through one, it will out of the other. They had planed to send a human inside a pot through and out it, even when anomalies were showing in the scans, Krei still went through with it to show the general that it was safe. But after the pot went in they lost contact with it and the second portal destroyed itself, while the other one became a vortex and sucked everything in.

The team's fiery of Krei being the masked man grew as they "realized" the reason why Krei had started the fire and stolen Hiro's Microbots, so he could take his technology back, but Yokai ended up being Professor Robert Callaghan and he escaped with the end of portal when Baymax had his healthcare chip reasserted into him. After Hiro calmed down and the team saw the rest of the footage, they realized why Callaghan wanted it: the pilot was his daughter, Abigail Callaghan and he blamed Krei for sending her into it.

As Krei was opening his new Krei Tech Building Callaghan used the microbots to capture Krei and to hold up the portal as it started to suck the building into it. Hiro later got the team to use the portal to their advantage as it sucks up the microbots. After Callaghen was catch and the team went to find cover until the portal destroys itself, Baymax picked up Abigail's life reading within the portal, meaning that she was still alive. Hiro and Baymax went in to save her and discovered it's void universe, as parts of Krei Tech floating around them. After the two found Abigail and were about to bring her home, Baymax's suit was damage and used his rocket fist (with his Healthcare chip clutched in it) to send Hiro and Abigail back, Hiro didn't want to leave Baymax in the void universe as the portal's shield was tearing it apart, but time was running out and it was the only for them to get Abigail Callaghan back home to their universe. The portal then exploded when the two got safely through and Abigail was sent to the hospital, so she way recover from the time sleeping in the portal.

Role in the Crossover
The portal may be gone, but fans still use it in science fiction based crossovers: and its possible that Hiro and Abigail aren't the only "ones" to get through the portal before it destroyed itself.