Tatta Hitotsu no Koto shika Shiranai

Fujinoki, an ordinary office worker, finds unexpected joy in the irregular calls from his elementary school classmate, Akaiwa. After 20 years without seeing each other, Fujinoki has no clue about Akaiwa's whereabouts or occupation. However, their peculiar phone-only friendship takes an unexpected turn!

(Source: Kodansha, translated)