Who can you romance?
Estelle is the romance option. Other characters can become close friends, but friendship does not make Mawuli, Best, or another character a romance route.
Start with Estelle’s story
Continue into Chapter 2, follow her messages, and take part in her story events. Her Heart Palace story and later relationship choices are related parts of her progression; this page is an overview rather than a dialogue-by-dialogue romance route.
If her second heart will not unlock
A particular theatre dialogue branch can lock the second heart unexpectedly. That bug is different from a normal rejection or a relationship event that has not triggered yet.
See Estelle’s second heart for the theatre choice and the Windows save workaround. For the puzzle route, use Estelle’s Heart Palace.