Osamake: Romcom Where The Childhood Friend Won't Lose (幼なじみが絶対に負けないラブコメ, Osananajimi ga Zettai ni Makenai Rabu Kome; "A Romantic Comedy Where the Childhood Friend Absolutely Will Not Lose"), abbreviated as Osamake (おさまけ), is a Japanese romantic comedy light novel series written by Shūichi Nimaru and illustrated by Ui Shigure. A manga adaptation with art by Ryō Itō has been serialized in Media Factory's seinen manga magazine Monthly Comic Alive since November 2019. An anime television series adaptation by Doga Kobo aired from April to June 2021.

Sueharu Maru is a seventeen-year-old high school boy who has never had a girlfriend. He lives next door to his childhood friend Kuroha Shida, a small and cute Onee-san type of girl with an outgoing character that frequently annoys him. One day, Kuroha confesses to Sueharu, but he immediately rejects her; Sueharu only has eyes for his first love, Shirokusa Kachi, who is a beautiful idol and an award-winning author in school. Shirokusa is indifferent to all boys in school but Sueharu, which makes Sueharu think that he might have a chance. When Sueharu decides to confess his feelings, he is devastated to find out that Shirokusa already has a boyfriend. Kuroha approaches Sueharu, offering to help him get revenge on Shirokusa and her boyfriend. Sueharu initially declines, wanting nothing to do with Kuroha, but eventually agrees to let her help him, thinking he might still have a chance with Shirokusa. However it turns out that Shirokusa also has feelings for Sueharu.

The names of the characters are references to characters in Fire Emblem: for instance, Maru, Shida, Kachi, Kai and Maria are named after Marth, Sheeda, Catria, Cain and Maria respectively. The names of the female characters include colors: for instance, Kuroha (lit. "black feather/wing"), Shirokusa (lit. "white grass"), Momosaka (lit. "pink slope/hill"), Asagi (lit. "pale/shallow yellow"), Midori (lit. "green"), Aoi (lit. "blue-i"), Akane (lit. "red sound") and Shion (lit. "purple garden").

Written by Shūichi Nimaru and illustrated by Ui Shigure, Osamake was published by ASCII Media Works, under its Dengeki Bunko, in thirteen volumes, released from June 8, 2019, to February 7, 2025.

A manga adaptation by Ryō Itō began serialization in Media Factory's Monthly Comic Alive in November 2019, with six tankōbon volumes were published so far.

A spin-off manga series illustrated by Mutsumi Aoki titled Osananajimi ga Zettai ni Makenai Love Come: Otonari no Yon-shimai ga Zettai ni Honobono suru Nichijō ("Daily Lives Where the Four-Sister Neighbour Absolutely Will Make You Warm") began serialization in Media Factory's Monthly Comic Alive on January 27, 2021. Three tankōbon volumes have been published so far.

An anime television series adaptation was announced on October 3, 2020. The series was animated by Doga Kobo and directed by Takashi Naoya, with Yoriko Tomita handling series' composition. Naoya also designed the characters. It aired from April 14 to June 30, 2021, on AT-X and other channels. Riko Azuna performed the series' opening theme song "Chance! & Revenge!", while Inori Minase and Ayane Sakura performed the series' ending theme song "Senryakuteki de Yosō Funō na Love Comedy no Ending Tema Kyoku" (lit. "An Ending Theme Song for a Tactically Unpredictable Romantic Comedy"). Crunchyroll streamed the series outside of Asia. Muse Communication has licensed the series in Southeast Asia and South Asia, and will stream it on their Muse Asia YouTube channel and Bilibili. The series ran for 12 episodes.

The light novel ranked fifth in 2020 in Takarajimasha's annual light novel guide book Kono Light Novel ga Sugoi!, in the bunkobon category.