Angela resides and works at Saint Mary's Convent in Tokyo. During the day, she takes confession and helps out at the local kindergarten.
Her other more senior nuns have become caught up in Angela's antics with Kosaku and take a vested interest in how things will turn out between them. The Mother Abbess however, vows to keep Angela safe from the heathen Kosaku.
Mother Abbess and Kosaku get off to a bad start as Kosaku doesn't have enough sense to treat her with the respect that a high ranking Catholic nun deserves. He calls her "nanny" and does things to generally annoy her, and she wastes no time in dousing him with water to let him know of her displeasure. Even though she is strict, she is very fond of Angela, and is doing her best to protect her, and keep her firmly on God's path.
The Meaning Behind the Name - 修院長
An abbess is a female abbot. Mother Abbess works and resides at Saint Mary's, which was named for Mary, the mother of the holiest Christian figure, Jesus Christ. The Japanese word for abbot is "修院長" (Shuuinchou). Kosaku often addresses her as "ばあや" (Baaya) which roughly means "nanny".