Someone's Girlfriend (Japanese: アイツノカノジョ, Hepburn: Aitsu no Kanojo) is a Japanese web manga series written and illustrated by Nikumaru [ja].

It has been serialized on Shogakukan's digital platform Sunday Webry [ja] since September 2022.

Written and illustrated by Nikumaru [ja], Someone's Girlfriend was first published as a one-shot on Shogakukan's digital platform Sunday Webry [ja] on November 27, 2021,[2] and started its serialization on the same platform on September 30, 2022.

[3] Shogakukan has collected its chapters into individual tankōbon volumes, with the first one released on February 10, 2023.

[4] The manga has been licensed for English released in North America by Seven Seas Entertainment.