By choosing the options seen on the Ending Directory page, following certain instruction will bring you to Tatsuki's true ending.
Tatsuki is trying to fly a plane for the second time and Hiroyuki Nishimura promises that he'll come by and see him again, they both board the plane afterwards. Hiroyuki seems scared at first, but keeps to his promise and stays on board with Tatsuki despite Midoriya giving him the chance to leave the plane.
A choice is purposed.
- A. What's That?
- B. What's This?
What's That: Hiroyuki and Tatsuki hear shouting from the distance, then comes Torahiko, with all your other friends too, they've come to see Tatsuki fly the plane, they're greeted by them, nearing the edge of the cliff once more and thinking they might fall, Hiroyuki is frightened, and everyone wishes them both to fly, luckily this time, hey begin to fly high into the sky just near the edge of the cliff.
Their friends feel extremely happy that the plane set off, and are now in joy to see that Tatsuki finally got his wings (metaphorically, of course!). Hiroyuki then begins to explain the detail of the sky whilst talking to Tatsu-nii.
Tatsuki asks Hiroyuki to close his eyes, Hiroyuki does as asks and then he is kissed in the midst of the sky, a long passionate kiss. Afterwards, they land perfectly.
They then have a talk with their friends about the original plane, the one that crashed, Tatsuki says everyone else should pay for the repairs of the plane and gets called names such as "Demon" and "Ogre". Tatsuki later says that he would like to build a house for him and Hiroyuki some day, which, Hiroyuki sees as his way of purposing to him.
August 30th
Hiroyuki is told about a meteor shower happening later that night, and since it's his last night in Waterfront he goes and sees it with his friend, the night ends with Hiroyuki and Tatsuki showing their complete affection for eachother.
August 31st
Hiroyuki says his goodbyes and leaves Waterfront, promising to come back every Summer and Winter (or easilly put, every holiday he has) until he's old enough to move out of the city and live with them in Waterfront.
Fin
What's This: Nishimura gets extremely curious and presses a big red button with a skull and crossbones on it, an alarm starts to sound and Tatsuki and Hiroyuki quickly try to escape the plane and fail, the explosion completely destroys Waterfront, including everyone inside, you, Tatsuki, Chuukichi, Torahiko, everyone.
The game then backtracks you to the beginning of the day.