Demon Slayer is a shonen action series with a strong emotional core, mainly centered around protagonist Tanjiro Kamado's sympathetic quest to restore Nezuko's humanity and Tanjiro's generous compassion for the demons he slays. Best of all, many of the Hashira are the same way and support Tanjiro personally, but Shinobu Kocho is an exception.
Shinobu Kocho certainly has her own sympathetic side, having lost her beloved big sister Kanae to a demon years ago, but she's too consumed by her self-centered thirst for revenge to do much more than fight demons in retaliation. While Kyojuro Rengoku, Tengen Uzui, and Mitsuri Kanroji have said and done much to support Tanjiro as a person and as a fighter, Shinobu lags behind – marking her as the least compelling Hashira so far.
Shinobu Kocho Doesn't Inspire Or Protect Demon Slayer's Heroes
While the nine elite Hashira weren't actually ordered to mentor or train Tanjiro's trio of heroes, several of the best Hashira still volunteered to support Tanjiro's squad with their words and actions alike, making them some of Demon Slayer's best characters. Kyojuro Rengoku gave his life protecting Tanjiro's team from Akaza, the Upper Moon 3, and shared inspiring words in his dying moments. Later, Tengen Uzui was a tough but fair guardian and coach for Tanjiro's team in the Entertainment District, and his inspiring character arc with his three shinobi wives flattered him immensely. Most recently, Mitsuri Kanroji the love Hashira volunteered to hold off Hantengu's strongest form to help Tanjiro, and she generously supported Nezuko on a personal level.
By contrast, Shinobu Kocho does her duty well as a Hashira, but little more. In her defense, she is highly preoccupied with justifiable anger and grief over Kanae's death, but even so, she outwardly lags behind the other Hashira and has done little to impress Demon Slayer fans. Her kind words to Tanjiro back in Season 1 merely reaffirmed what Tanjiro was already doing for Nezuko's sake, and she even tried to kill Nezuko when they met in Rui's spider forest.
Shinobu also didn't teach Tanjiro's team much of anything, with Aoi and Kanao Tsuyuri handling Tanjiro, Inosuke, and Zenitsu's training at the Butterfly Estate. By now, Shinobu is overdue to say or do something to motivate and inspire Tanjiro's team, even if she doesn't have in-universe obligations to do so. For the sake of her character's likability and to give her some relevance, Shinobu Kocho must do more.
Tanjiro & Kanao Can Bring Out The Best In Shinobu Kocho
Shinobu Kocho hasn't said or done much to bring out the best in Tanjiro's team or even her apprentice, Kanao Tsuyuri, so it might go the other way around. All things considered, Shinobu needs more support than they do, given her grief and rage, so Tanjiro can pay it forward and support her however he can. Tanjiro owes a lot to the Hashira, mostly through Kyojuro, Tengen, and Mitsuri, so he can return the favor with Shinobu. That's consistent with Tanjiro's famously empathetic and supportive ways, even if Tanjiro has little left to prove to audiences, so he should do it. Kanao Tsuyuri can do the same, repaying Shinobu for taking over her training after Kanae's untimely death. Shinobu may be tense and angry, but she still made time for Kanao, the quiet girl whom Shinobu once scorned.
With the final battle against Muzan Kibutsuji and the three remaining Upper Moons looming, Shinobu might lose herself to her reckless rage and get sloppy in her quest for revenge. So, she needs Tanjiro and Kanao to be for her what Kyojuro and Mitsuri were for the Kamados, and temper that furious fire in Shinbou's heart. That should benefit Shinobu as a fighter and as a person, and best of all, surely a grateful Shinobu would return the favor someday and become the next Mitsuri Kanroji. All that should help boost Shinobu's standing in the eyes of Demon Slayer fans, and change her from a somewhat gimmicky Hashira to an inspiring, wonderful big-sisterly warrior whom any Demon Slayer character or fan can love. There must be more to Shinobu Kocho than poison and revenge.