with friends she'll occasionally reference 'my cousin' in a sentence and nobody every knows who she's talking about, they just all blur together from a distance
She's doing bizarre liquid alchemy with five different finely tuned instruments and may have committed some sins against nature to try and genetically reverse-engineer the correct kind of coffee bean.
...I feel like eventually she somehow creates something that perfectly nails the taste and texture of Good Coffee, but also it turns your tongue purple for a couple days.
Mercy will recognize any cousin she's been introduced to in person, but immediately loses track of who's who in any long, complicated story about family shenanigans, so she just shrugs and goes with it.
she just intentionally gets it wrong sometimes to fuck with erina