If you are referring to the 23rd volume of the Light Novel, titled the story reaches a critical turning point for the Shiba siblings:
Tatsuya begins focusing on the ESCAPES project , aiming to provide a way for magicians to be useful to society beyond just being weapons of war. Quick Facts MahoukaRettousei6HD23:40 Min
The National Defense Force and the Magic High School students defend against a surprise invasion by the Great Asian Alliance. If you are referring to the 23rd volume
This volume further explores the fallout of Tatsuya and Miyuki’s engagement, which was officially announced to the Ten Master Clans to secure their position within the Yotsuba family. The world begins to fear Tatsuya's "Material Burst"
The world begins to fear Tatsuya's "Material Burst" ability, leading to international pressure to isolate him.
Suzune Ichijou questions Tatsuya's emotional state and his seemingly cold efficiency in combat, highlighting the "mental interference" experiments performed on him by the Yotsuba family. Light Novel Volume 23: Isolation Arc
Near the end of the episode, the focus shifts to Tatsuya Shiba's overwhelming power as he begins to take a more active, lethal role in the defense, setting the stage for his reveal as a "Strategic-Class Magician".