"Lord Esselin have mercy on me..." ~ Archpriestess Choir
Esselin is a god mentioned during Momodora: Reverie Under the Moonlight. He used to be worshiped by the people of Karst City, but by the time of the story events most citizens have lost their hope in the gods, save for the zealous, fanatical nuns of the Forlorn Monastery, including Pardoner Fennel and Archpriestess Choir.
It's unknown whether the people's faith in Esselin is restored after the events of the game or whether they move on to worship Kaho and the gods of Lun.
The character, and faith in him are directly modeled after the Catholic Church, from aesthetics to doctrine and monotheism.