Dodgeball Academia does feature multiplayer, just not in the main game. The campaign for the game was designed to be a single-player experience from start to finish. So if you want to play the campaign with a friend, they will have to sit on the sidelines.
Where multiplayer comes in is a mode separate from the main game. This mode solely lets you battle against your friends via intense dodge ball matches. This multiplayer mode is limited to two players only, so you will have to take turns if there are more players.
Related: How many players can you have on the court in Dodgeball Academia
While the single-player campaign offers a more strategic approach to the gameplay, this multiplayer mode takes on a more chaotic approach. Both players take opposite sides of the court and face one another in dodge ball deathmatch. Both players can select their teammates as well as what game type to play.
The multiplayer mode is limited to offline play online as there is no online functionality in Dodgeball Academia. This means you will have to meet up with your friends to play intense dodge ball matches. This also means that you can talk trash in person when you throw a ball in their faces.
For more information on Dodgeball Academia, check out How to switch characters during a match in Dodgeball Academia and How to change your team in Dodgeball Academia on Pro Game Guides.