Other known Cancer
Violet Evergarden - Violet Evergarden
Nami - One Piece
Subaru Oozora - VTuber
Shouyou Hinata - Haikyuu
Izuku Midoriya - My Hero Academia
Sailor Moon - Sailor Moon
Himeno Awayuki - Pretear
Akko Kagari - Little Witch Academia
Akatsuki - Log Horizon
Kaoru Kamiya - Rurouni Kenshin
Houki Shinonono - Infinite Stratos
Touka Kirishima - Tokyo Ghoul
Aoi Sakuraba - Ai Yori Aoshi
Hiiragi Twins - Lucky Star
Canada - Hetalia Axis Powers
Popura Taneshima - Working!!
Hideri Kanzaki - Blend S
Lucia Nanami - Mermaid Melody Pichi Pichi Pitch
Yuri Tanima - Wedding Peach
Shunsui Kyoraku - Bleach

Cancers can effortlessly pick up the energies in a room and are highly sensitive to their environments, as well as extremely self-protective, while cold at first they will eventually open up.
Ruri spends a good portion of the anime as being the straight woman of the crew, she prefers to avoid madness and would rather just quietly get on with her job but as she develops she opens up more and eventually becomes the captain to a new team.
Ruri's journey from Science Officer to Captain is definitely the path of a Cancer.