Eri had first met Shiki when she saw her creating Mr. Mew. The two talked and later on, they became best friends. As time grew on, Shiki became more and more jealous of Eri, because Eri was supposedly prettier, smarter, and had lots of friends. Shiki then began to hate herself, because she felt that there was nothing special about her.
One day, Shiki couldn't come up with a good design so Eri told her that she wasn't meant to be a designer. Even though Eri meant it as an encouragement (as while Eri was the designer, Shiki was an incredibly talented seamstress who brought the designs to life), Shiki took it the wrong way and was hurt. Eri was upset and sad when Shiki died and would always regret what she told her.
However, due to Shiki's entry fee in the Reapers' Game, Shiki's true appearance was taken away and she was replaced with Eri's appearance. Eri is first seen in Week 1 Day 6, talking to another friend, Mina, about how she wished she had never hurt Shiki's feelings and how they would always be best friends. Eri then talks about Shiki's amazing clothes-making skills and how she wanted them, thus giving Shiki the strength to go on and win. Shiki also discovers that she valued who she was the most, and winning the Game to see Eri once more became Shiki's goal.