The city lights blurred outside the train window as returned home after three years away. He was anxious to see how much had changed, especially his younger sister,

Providing more context will help me give you a meaningful, in-depth response.

Medium:

Primarily identified as a digital release, likely a visual novel or adult-oriented manga/translated story.

Netorare (NTR):

Focuses on the perspective of the "victim" who loses their partner, often highlighting feelings of betrayal and despair.

The silence returned, but this time it was filled with the reality of their situation.

Transgression:

Breaking social taboos (like the "little sister" or "betrayal" tropes) provides a safe, fictional way to explore intense emotions that are off-limits in reality.

• Blur Boundaries: Raise questions about appropriate boundaries and expectations in sibling relationships.
• Elicit Social Judgment: Attract criticism or judgment from those who do not understand the netori dynamic.