Put it down to diminished expectations or what have you, but there’s a surprising delicacy to “Midnight Sun,” a teen weeper built around Bella Thorne.

You may know what to expect, if you’ve seen “A Walk to Remember” or “Everything, Everything” or even “The Fault in Our Stars.” But all involved give this picture a sympathetic shot, even if the script flails and fails miserably in concocting an ending that feels earned, honest and as graceful as what comes before it.

In this adaptation of a 2006 Japanese melodrama, Thorne plays Katie, a teen who has spent her whole life indoors — at least during daylight hours. She suffers from Xeroderma pigmentosum, “XP,” a rarer-than-rare genetic disorder that makes the sun deadly to her.

She grew up as “the vampire” next door, when the other kids in her corner of Washington thought of her. But that was years ago. The only people she spends time with are her doting dad, played by Rob Riggle at his sweetest and most PG, her BFF the irrepressible Morgan (Quinn Shephard, adorable) and the guy who runs the train station late at night, where she plays guitar and sings for passengers who get off the last commuter trains of the evening.

Then there’s Charlie, the hunky high school swimmer (Patrick Schwarzenegger) whom she watches go to school “every day, and yet he had no idea I even existed.”

Until that fateful night when she drops her songwriter’s journal and he picks it up.

It says something of Thorne’s skill that, as an almost certainly-jaded former child star (“Shake It Up”) who seems to court provocative web attention as a means of “building her brand,” that she’s able to summon up the awkwardness and under-socialized shyness necessary to pull off her early encounters with her dream boat.

“Holy pregnant cow!”

Schwarzenegger has barely a hint of his Dad in his looks and demeanor, and a disarming charm is the result.

The adaptation gives this story the expected high school touchstone moments — Katie’s first high school party, a post-graduation bacchanale cut into a montage as bouncy as a game of beer pong. A romantic trip to Seattle, a hint of how each gives something to the other, all tossed in for good measure.

Did I mention she doesn’t tell him she’s sick? She’s got her reasons. “When you tell somebody you’re sick, they stop seeing the real you.”

Director Scott Speer (“Step Up” sequels) and screenwriter Erik Kirsten don’t hide the inevitable and can’t get out of the drawn-out ending to save their lives. But they give Thorne some nice showcase moments, make her plaintive but pleasant singing voice fit the story and have the good sense to make Charlie’s summer job involve a marina.

What’s more romantic than a sailboat?

If you’re old enough to remember “A Walk to Remember,” there’s nothing here that will surprise you enough to warrant skipping this week’s “This is Us.” But if you’re still a dewy-eyed teen fresh out of going “Awwwww” at the out-of-date coming-out romance “Love, Simon,” there’s nothing wrong with stuffing a few tissues in your pocket and bracing for, if not a good cry, at least the sniffle or two “Midnight Sun” promises.

MPAA Rating: PG-13 for some teen partying and sensuality.

Cast: Bella Thorne, Patrick Schwarzenegger, Rob Riggle, Quinn Shephard

Credits:Directed by Scott Speer, script by Eric Kirsten ,based on the 2006 Japanese film screenplay by Kenji Bando . An Open Road release.

Running time: 1:31