Rumi Ōkubo is a Japanese voice actress born on September 27, 1989, in Ehime Prefecture, who was raised in Saitama Prefecture. She is affiliated with the talent agency 81 Produce. Standing at 150.3 cm tall with blood type A, she has been active in the voice acting industry since her debut in 2009.

Ōkubo decided to pursue voice acting after being inspired by the anime series Pokemon and Sorcerous Stabber Orphen, noting the performance of voice actress Mayumi Iizuka. To enter the field, she attended Tokyo Announce Gakuin (also known as Toho Gakuen). While still a student in 2009, she participated in the third 81 Produce audition, where she won an excellence award. This achievement led directly to her first professional roles, including a minor part in the anime Whispered Words, marking the start of her career.

Her early career saw a steady increase in prominent roles. In 2011, she landed her first regular role as Kaho Hiiragi in Freezing and her first leading role as Suguri Kinoshita in Happy Kappy. That same year, she began voicing two of her most enduring characters: Chinatsu Yoshikawa in the long-running comedy series YuruYuri and Ako Shirabe, also known as Cure Muse, in Suite Precure. Her performance in YuruYuri, in particular, helped establish her as a fan favorite. She continued to gain recognition with leading roles such as Tsumiki Miniwa in Place to Place in 2012 and Yuzuko Nonohara in Yuyushiki in 2013.

In 2013, Ōkubo received the Best Rookie Actress award at the 7th annual Seiyu Awards, sharing the honor with Kaori Ishihara. This accolade cemented her status as a rising talent in the industry. Throughout her career, she has demonstrated significant versatility, taking on a wide array of characters across many popular franchises. Her notable roles from the 2010s include Nobunaga Oda in Sengoku Collection, Hibachi in Mushibugyo, Kazuki Ferrari in Galilei Donna, Nona in Death Parade, and the voice of the Rider-class servant Astolfo in Fate/Apocrypha. She has also been a consistent presence in long-running franchises, voicing Mia Ageha across the Pretty Rhythm and PriPara series, Cleao Everlasting in various seasons of Sorcerous Stabber Orphen, and Soka in That Time I Got Reincarnated as a Slime and its spin-off, The Slime Diaries.

In the 2020s, Ōkubo has continued to secure major roles in high-profile anime. Her recent work includes Nana Hiiragi, the titular character in Talentless Nana, Lola in The Hidden Dungeon Only I Can Enter, Sharon Holygrail in Engage Kiss, Omoharu Nakanaka in Komi Can't Communicate, Enome in Immoral Guild, and Nell in Reincarnated as a Sword. In 2023, she gained significant international attention for her role as the internet-savvy MEMcho in the hit series Oshi no Ko. She has also been cast as Nene Himekawa in the adaptation of Tune In to the Midnight Heart. Beyond these roles, she has provided voices for numerous other anime including Skeleton Knight in Another World, My Home Hero, Sweet Reincarnation, and No Longer Allowed In Another World.

Beyond her anime work, Ōkubo is also known for her involvement in music and radio. She has been a member of several seiyuu idol and music units related to the series she has starred in, most notably the Nanamori Chu☆Gorakubu unit from YuruYuri and B Komachi from Oshi no Ko. She has also served as a host on the radio program Chaldea Radio Station Plus, which is related to the Fate franchise. Her hobbies include逛街 (shopping) and creating illustrations, a skill she developed as a member of her middle school art club.