I'm a Childhood Friend, and I Want to Remain a Supporting Character, but for Some Reason, I Became the Heroine's Love Interest

When Mashiro Yukizuki is reincarnated into the world of a gal-game as “Ryona Amezuki,” one of the heroines of the game, she decides she wants to live as inconspicuously as possible. But when she helps to rescue “Ririnri Hinahoshi” from being harassed by a man downtown, she finds herself in the middle of a love affair. Now everything she tries backfires, as Ryona finds herself attracting the love interest of more and more heroines… (Source: Digicata, translated)