There was some inconsistent information regarding which episode of Joy of Life where the Eldest Princess sacrificed herself to the Crown Prince. Some search results showed that the plot happened in episode 15, while others showed that it happened in episode 22. Due to the inconsistent information, it was impossible to determine the exact answer. It is recommended to watch TV series or related commentary videos to obtain more accurate information.

The plot of the Eldest Princess and the Crown Prince appeared in the 15th episode of Joy of Life.
The scene of the Eldest Princess sacrificing herself to the Crown Prince happened in the 15th episode of the TV series Joy of Life.
The plot of the eldest princess and the crown prince in the TV series "Celebrating Years" appeared in episode 15.
In the TV series Joy of Life, there was no plot of the Eldest Princess sacrificing herself to the Crown Prince. In the original novel, the plot of the Eldest Princess sacrificing herself to the Crown Prince took place in chapter 86 of the sixth volume. Therefore, it was impossible to determine which episode the Eldest Princess and Crown Prince were in.
The plot of the Eldest Princess and the Crown Prince appeared in the 15th episode of Joy of Life.
The plot of the Eldest Princess and the Crown Prince appeared in the 15th episode of Joy of Life.
The scene of the Eldest Princess sacrificing herself to the Crown Prince appeared in the 15th episode of the TV series Joy of Life.
The Eldest Princess and the Crown Prince were in the 15th episode of the TV series " Celebrating Years ".
The plot between the Eldest Princess and the Crown Prince took place in the 15th episode of Joy of Life.
The plot of the Eldest Princess and the Crown Prince appeared in the 15th episode of Joy of Life.
The scene of the Eldest Princess sacrificing herself to the Crown Prince appeared in the 15th episode of the TV series Joy of Life.