When the enemies are in a number advantage and the bullets are falling like rain, the two fighters can combine by getting attached horizontally and the defense mode will be awoken. A shield would be created around the combined fighters and it could protect the larger fighter from the bullets. Keep in mind though that the shield could not do much against a crush. You may divide the fighters simply by sliding your fingers in different directions.
These two fighters can also combine vertically and become something more aggressive. Attach the head of one fighter with the end of the other one could trigger the offense mode. In this mode, these two fighters could transform into a huge fighting robot and only one punch of it will be enough to blow everything in the screen up into pieces.
The pilots of the fighters are connected so when one fighter is crushed or blew up, the pilot of the other fighter would become so sad that he would literally beat himself to death. So try to keep the safety of both fighters in mind.
Your battle happens in an abandoned space station tunnel and your enemies are all kinds of weird aliens. They will come back faster and stronger each time you kill them so show no mercy.
The fight has begun, release the fighters.
Best to play on a tablet though.