It is at Hiroo 5-16, 220 m from Hiroo Station, which fits with the fact that in the first episode Rintarō uses that very station.
ℹ️ A residential street with working businesses: you just pass through.
🚉 Hiro-o · 3 min walk
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The alley in front of the stonemason's, recognised by the three shop awnings lined up on the left-hand side, in the flashback where Shōhei complains to Rintarō in class (episode 2). Nearby, below the threshold: the 広尾児童遊園地, 95 m to the south-west, which the two pass on their way back from studying in episode 4; and, 150 m to the west, in front of the 広尾ハイツ, where in episode 5 Saku (who has just argued with Rintarō and gone home alone) is stopped by Shōhei and Yoda.
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Sources: seichi-shioricho.com · animepilgrimage.com · note.com
Nearby
Hiroo Station200 mphoto by Photonica at Japanese Wikipedia · CC BY-SA 3.0
Japanese Red Cross Medical Center — Hiroo500 mphoto by Syced · CC0
Hiroo Kita Park700 mphoto by Syced · CC0
Kōgai Park800 mphoto by Syced · CC0