Its just a little cutscene! You can only get it if Yuki's affinity hits a certain threshold.
Easiest way to get there would be to,
1. Make sure to go help him when he's fallen.
2. Visit Zach, annoy him, or be friendly, it doesn't matter.
3. Visit Yuki, when talking about the sculpture, pick option, "beautiful"
4. When asked about Zach, do NOT lie.