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Seven years after a lab explosion, Chan returns home for work and unexpectedly meets Haran again.

Chan sees that Haran is frozen in winter and suggests a three-month trial friendship.

Haran rejects Chan's three-month friendship offer, but Chan is undeterred.

As Chan and Haran grow closer, a mysterious sound begins to haunt him, revealing gaps in his memory.

Chan and Ha-ran find a Gyeongju escape but a resurfacing memory puts Chan in a brewing storm. Unbeknownst to Ha-ran, Chan is drawn into a brewing storm.

Chan's sudden exit for the U.S. leaves Ha-ran reeling. As longing sets in, the three sisters clash and Na-na faces an unexpected incident.

Chan and Ha-ran reunite after his U.S. return. At a SHIM party, their bond grows while Chan starts recording his resurfacing memories.

Ha-ran helps Chan reveal his father's watch secret. After their reconciliation, Ha-ran wins an award but meets a shocking face at the ceremony.

Chan's unintentional lie about the fountain pen weighs on his conscience. To stay close to Ha-ran, he must decide if the truth is worth the risk.

Chan's envy of Su-jin and Ha-ran grows. As Ha-ran celebrates Chan’s birthday, she moves past her "winter" while Nana makes a choice in Chuncheon.

Ha-ran, who learns Chan's secret from seven years ago through the "1-Inch of Memory" notebook, falls into confusion upon realizing that even the fountain pen was a gift he had prepared.

After their trial ends, Haran learns the truth. Chan has vanished, but discovering his feelings, she goes to find him.