The following contains spoilers for Demon Slayer: Kimetsu No Yaiba Chapter 168, "Never Disappear" by Koyoharu Gotoge, available now in English via Viz Media.
There are a total of ten ranks within the Demon Slayer Corps, beginning at Mizunoto and ending at Kinoe. The Hashira are the most powerful and well-accomplished of the Corps, ranking at a level entirely off the scale. To get this title, a Demon Slayer must reach the level of Kinoe -- then either defeat 50 demons or slay a member of the Twelve Kizuki.
Two members of Demon Slayer's current nine Hashira achieved the title for very similar reasons. Both the Insect Hashira, Shinobu Kocho, and the Wind Hashira, Sanemi Shinazugawa, battled their way to the highest and most respected position in the Demon Corps after losing their family to demons.
Demon Slayer's Shinobu and Sanemi Are Both Fueled by Hate
The Wind and Insect Hashira alike are angry at demons, but also at themselves. When Sanemi was a child, his mother became possessed by a demon and killed five of his siblings, leading to the Hashira killing her to save himself and his younger brother. Shinobu likewise lost her family to demons, having both parents killed at a young age, then losing her older sister Kanae -- the late Flower Hashira -- in battle with an upper moon. The pair are justifiably angry at demons for being responsible for their losses and were motivated to become stronger to avenge their family's deaths.
However, the two Hashira are also angry at themselves; Shinobu is furious that she wasn't strong enough at the time to fight alongside her sister and save her life, while Sanemi is understandably upset at having to kill his own mother in self-defense. Because of this, the two have pushed themselves relentlessly to get to the level of Hashira purely out of spite, anger and revenge.
The Insect Hashira Internalizes Her Rage
The main difference between Shinobu and Sanemi is how they process their anger throughout Demon Slayer. Shinobu internalizes hers, successfully controlling it most of the time. She'll occasionally have a rage-induced outburst at a demon, but mostly the Insect Hashira is a model mentor for younger demon slayers. However, internalizing all her negative emotions toward demons has its downsides.
Shinobu's anger has festered inside her for her entire life, and she hates that part of herself. In some cases, the reason the Hashira could never forgive and empathise with demons as Tanjiro Kamado does is because of the amount of unbridled anger inside her. Because of this, Shinobu was never able to truly avenge her sister, as she would've had to learn how to forgive demons to properly process Kanae's death.
The Wind Hashira Externalizes His Anger
On the other hand, Sanemi's rage is constantly on show in Demon Slayer. He is obviously angry at the world and wants everyone to know it, and this is shown when he first met Nezuko Kamado. When she and Tanjiro were introduced to the nine Hashira, Sanemi showed an instant dislike to Tanjiro's younger sister. Without even knowing her, the Wind Hashira instantly despised and taunted her, trying everything to get her to attack him and prove to his peers that she was just like other demons.
While Shinobu is liked by the majority, Sanemi is generally disliked by most people he meets. His externalized anger makes him grumpy, rude and irritable, and he'll take out his anger on anyone, not just demons. Sanemi's unprocessed rage has even made him push his younger brother Genya away, making his sibling face the brunt of his anger.
While both Hashira have a similar background and reason behind pursuing their impressive rank, Sanemi and Shinobu have followed very different paths. Despite their similarities, it's unlikely the pair will ever be friends, even though they could help one another through their respective trauma. Future arcs of Demon Slayer may see the Wind and Insect Hashira avenge their families and learn to process their anger in healthier ways, not hurting themselves or those around them anymore.