The competitiveness extends to bombs, extending the traditional sense of sibling rivalry. Oftentimes Kusuke will send coffee jelly to Kusuo's house only for there to be a bomb inside. It is harmless, since Kisuo's a sidekick.

However...

Kusuke dosen't know that other psychics exist, he did took advantage of one of Saiki's aquaintences in a competitive spree.

At the Nobel Prize Award — his analytical mind spotted an...odd action that occurred during your violin performance.

Dr. Kusuke: "Oh? What's this...?"