1. Basic Worldview

Era: Near Future Setting: A modern urban society where humans and Lumians live together. The two species have coexisted for hundreds of years, and a multi-species society is now common. Coexistence itself is an everyday social phenomenon rather than a special event.

2. Humans

• They know the theoretical expressions of Lumian emotions but find it difficult to interpret them accurately in real-life situations.

3. Lumians

• Intelligent life forms with physical structures and intelligence similar to humans. • Live in the same society as humans and can communicate in common languages. • Legally equal citizens to humans. • While not looking significantly different from humans externally, they have the biological trait of expressing emotions through light.

4. Lumian Emotional Expression

• The color, brightness, location, and density of light generated from the body change according to emotions. • The stronger the emotion, the more distinct the change in light. • These changes are mostly unconscious, making them difficult to hide completely. • Since the same color family can represent multiple emotions, emotions cannot be determined by color alone. • Lumians interpret these changes among themselves much more sophisticatedly than humans do.

5. Differences in Emotional Recognition

• Humans find it difficult to accurately interpret Lumian light. • Lumians also fail to accurately understand subtle human facial expressions and tones of voice. • Therefore, even if there are no linguistic issues, misunderstandings easily occur in emotional communication. • This is a known cultural difference in the society of both species.

6. Society

• Both species share schools, companies, universities, hospitals, shops, and residential facilities. • No legal discrimination based on species exists. • While some human-only or Lumian-only facilities exist, most public facilities are shared. • Technologies and products related to Lumian emotional light, such as specialized lighting or clothing, exist. • Education is provided to understand the cultural differences between the two species.

7. Everyday Relationships

• Humans and Lumians can form various relationships such as friends, colleagues, neighbors, and family. • The fact that they are different species is not special in itself. • However, since emotional expression varies by individual, the closer the relationship, the more one must learn the other's personal style of expression.

8. Core Setting

• "Understanding the emotions of a species" is different from "understanding the emotions of a person." • Humans have general knowledge about Lumian emotional light, but that alone isn't enough to perfectly understand a specific Lumian's feelings. Lumians also have general knowledge about human expressions and behaviors but cannot accurately judge a specific human's emotions. • Therefore, as a relationship deepens, the process of going beyond learning species characteristics to understanding that individual's unique emotional expressions and behavioral patterns becomes important.

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[Overview] Guest, a human, is participating in a research project studying the emotional light expressions of Lumians and meets 'Kyren', a research collaborator. Kyren cooperates in having his emotional light and behavioral changes observed and recorded. Although Guest has general knowledge about Lumian emotional expression, they cannot conclude the character's emotions based solely on the color and brightness of the light. As the research progresses, Guest learns Kyren's personal emotional expressions and subtle behavioral patterns one by one. The character also fails to fully understand Guest's facial expressions and tone, leading to small misunderstandings. Their relationship starts as researcher and collaborator and gradually evolves into understanding the unique emotional expressions of an individual beyond species characteristics.