Tomoe Udagawa, a third-year at Haneoka Girls' High School, drums for the band Afterglow. She is the older sister of Ako Udagawa, Roselia's drummer, sharing a relationship that balances rivalry with mutual support despite their contrasting personalities and appearances. Notably taller than Ako, Tomoe has maroon hair and turquoise eyes, favoring mature, punk-inspired outfits featuring studs or chains, reflecting a relaxed yet cool aesthetic compared to Ako's shorter stature and warmer eyes. Her hair was shorter in middle school and worn in a long ponytail during earlier childhood.

Deeply woven into her community, Tomoe has performed taiko drumming at local shopping district festivals for over a decade, earning admiration for her skill and highlighting her connection to traditional music. She previously worked part-time at a fast-food restaurant with bandmate Himari Uehara and now works at Galaxy Ramen alongside Masuki. Her friendships extend to Saaya Yamabuki outside Afterglow.

Reliable and candid, Tomoe refuses to hold grudges or speak negatively about others. She acts as a stabilizing force within Afterglow, preventing conflicts and providing emotional support. Despite her generally mature demeanor, a hotblooded streak flares when confronting perceived threats to those she cares about, occasionally backfiring. She shares a unique mental wavelength with characters like Kasumi and Kokoro, surprising others with this unexpected compatibility. While sometimes perplexed by Ako's energetic behavior, she consistently supports her sister's endeavors.

Her interests include collecting landscape photo books from around the world and reading. Before performances, she energizes herself by chanting "soi-ya." A shared voice line—"When's the next performance?"—with Moca Aoba led to a humorous body-swap premise during a Halloween event where they impersonated each other after a ride accident. Tomoe and Kaoru are regarded as Haneoka's most popular students, though Tomoe remains modest about this. She acknowledges Himari as the person who understands her best.

Her name carries symbolic meaning: "Udagawa" combines characters for "universe," "field," and "river," while "Tomoe" references a swirling water design, historically linked to archer's wrist protectors and serpent imagery. Her drumming style and community role reinforce her identity as a grounded yet passionate presence within Afterglow and the BanG Dream! universe.