Heundeullineun Segyelobuteo

Eunsae is an ordinary student who happens to meet her alternate self in her dream one day. Eun-i and Sae-i are both Eunsae, just from parallel universes! After a year of regularly meeting up in their dreams, Eun-i makes a tempting offer: to switch places and jump into each other's universes for a week. Sae-i, having been envious of Eun-i's perfect life, decides to accept the offer. However, Eun-i is nowhere to be seen when the promised week is over. Will Sae-i be able to keep pretending that she’s Eun-i until she can return to her own world?

(Source: WEBTOONS)