The protagonist is a normal high school girl who was born in the Sacred Bird Cosmos. She and many other girls act as school representatives for a field trip to Holy Land the day after her seventeenth birthday. Like the other girls, she is asked by the Sacred Guardians to walk through a series of doorways. Her path ends at a mystical stone slab which shimmers in her presence. Moments afterwards, a spirit takes the form of her treasured childhood doll to inform her that she is the legendary étoile, or a celestial messenger for the cosmos. Her mission is to help nurture the Sacred Beast Cosmos's growth within a year.

The player can name their protagonist and assign her birthday and bloodtype at the start of each game. Choose whichever doors and text options from the introduction sequence to slightly alter starting Intimacy ratings with the romanceable characters. The protagonist can move freely between the Sacred Bird Cosmos, Arcadia (Celestia) and the Sacred Beast Cosmos.

Main story events advance only when the player focuses on the cosmos. The general gameflow for completing the main storyline is a repeated cycle of steps:

Receive Sacrea from Sacred Guardians.
Distribute Sacrea to Sacred Beast Cosmos until a planet's culture develops.
Pacify the Sacrea Spirit which emerges.
Visit the Guardians-to-be three times and convince them to come to Holy Land.

If the player wishes to see the good default ending and/or romance every character, they will need to repeat the recruiting cycle nine times. Traveling between planets in the Sacred Beast Cosmos requires the protagonist to board the Flying Ship, Aurora; the captain will inform players of the time needed for a one-time trip to their highlighted destination before departure. The time needed for fostering the cosmos may negate romance events if the player plans poorly.

Nineteen characters can be romanced: the Sacred Guardians for both cosmoses and Arios. Arios is available in subsequent playthroughs. The player must have at least 2 unused, one Sacred Beast guardian and must visit Rachel on Fridays in order to see him. Visit him three times and select the correct text options to unlock the chance to romance him like other characters.

Intimacy and Affinity are the only two attributes for affecting a character's affections for the protagonist. Lovelove Flash, the "Charm" option at Sacred Beast's House of Divination, continues to be the only way of changing Affinity. étoile increases the number of opportunities for boosting Intimacy between a male character and the protagonist.