You can only unlock Shape of Love in Lost Ark after discovering Mokoko Village. It has a time limit and three different locations in Tortoyk to visit. After each new investigation, the time limit gets reset to a new time, so follow the guide closely.
Where is the Shape of Love Hidden Story?
First Hidden Story
Sweetwater Forest is the setting for the first part of this Hidden story. It's in Trampled Flower Field, west of Sweet Fruit Forest and south of Mountain Forest Trail. It's in front of a giant boot. Investigate the tip of the shoestring. The timer starts at 10 minutes.
Second Hidden Story
You can find the second part of this Hidden story in Sweetwater Forest. It will be east of Mokoko Farm, south of Sweet Fruit Forest, and southeast of Trampled Flower Field. You can find it in front of a giant pair of glasses. Investigate beneath the crack on the left side of the glasses. The timer will reset to 10 minutes.
Third Hidden Story
You can find the third part of this Hidden story in Skyreach Steppe. It will be east of Rocky Forest Hill, southeast of Pirate Post. Walk along the river heading east until you reach the top of the waterfall. You should investigate the southern end of the river where it meets a rock as soon as possible, since this area will be infested with enemies.
For more information on Lost Ark, check out Should you dismantle your equipment or sell it in Lost Ark? and Where to farm Levataonis Core in Lost Ark? on Pro Game Guides.