You can typically find this title on major Japanese digital storefronts. If you are looking for the official release, check:
The "Colored Portable" version represents a modern shift in how manga is consumed. Here is why this specific format is trending: ore ga mita koto no nai kanojo colored portable
The title follows the story of a protagonist’s encounter with a mysterious and captivating woman. While it began as a series of doujinshi (self-published works), its popularity led to various digital adaptations. The "Colored" versions are particularly sought after, as they enhance Shinozuka Yuuji’s detailed art style with a full professional palette, elevating the narrative experience from standard black-and-white manga to a more immersive visual novel-like format. You can typically find this title on major