Kasim, also known by his former adventurer title Sky Shatterer, is a significant supporting character in the story. He is an archmage who once journeyed as part of an adventuring party alongside Belgrieve, Satie, and Percival. The group shared many adventures together until Belgrieve was forced to retire from his adventuring career due to a debilitating injury that cost him his leg. After Belgrieve's departure, the remaining members attempted to continue as a party without him, but the dynamic had changed, and they eventually grew apart due to their differences.

Kasim continued his career as an adventurer and ultimately rose to the prestigious rank of S-Rank, a testament to his considerable power and skill. However, despite achieving this elite status, he found the experience hollow and unfulfilling without his original comrades by his side. This dissatisfaction with the adventurer's life eventually led him to retire from the profession altogether.

Following his retirement, Kasim fell on hard times and resorted to committing petty crimes. These included minor offenses such as dining and dashing, failing to pay for his drinks, and getting into brawls for small sums of money. For these actions, he ended up imprisoned in the city of Estogal. While he claimed his incarceration was for something as minor as skipping out on a restaurant bill, the precise reason remained ambiguous. During his time in prison, he struck up an unlikely friendship with Liselotte, entertaining her with tales of his past adventures in exchange for alcohol.

Kasim's role in the main narrative is deeply tied to his past relationship with Belgrieve. He is described as one of Belgrieve's closest friends from their adventuring days, though the two had lost touch for many years. Fate intervenes when Angeline, Belgrieve's daughter and an S-Rank adventurer in her own right, encounters Kasim. A character named Francois uses the imprisoned Kasim to test and demonstrate Angeline's overwhelming strength in battle. Upon learning that the powerful young woman before him is the daughter of his former friend Belgrieve, Kasim forfeits the fight. Wracked with uncertainty about whether his old friend would still consider him a comrade after all this time, Kasim nevertheless agrees to travel with Angeline to Orphen City, a journey that ultimately leads to a long-awaited and emotional reconciliation between the two former party members. This reunion is a pivotal event, mending a rift that had persisted since the original party disbanded.

In terms of personality, Kasim is portrayed with a sense of regret for his past actions and a deep, though insecure, affection for his old friends. When asked if he considers Belgrieve a friend, he affirms he does, but qualifies it by adding, if Belgrieve still thinks so anyway, revealing his fear of being rejected after their long estrangement. This insecurity is resolved when Angeline confidently states that her father is not so petty as to hold a grudge. His period of petty criminality suggests a man who became aimless and disillusioned after the loss of his social and professional purpose, a stark contrast to his former glory as an S-Rank mage known as Sky Shatterer. His primary motivation in the story is to reconnect with his past and find a new sense of belonging, which he achieves by rekindling his friendship with Belgrieve.

As an archmage and former S-Rank adventurer, Kasim's notable abilities lie in his powerful magic, a fact that makes him a formidable figure despite his later decline into petty crime. His reputation and power were such that he was sought out specifically as a challenging opponent to put Angeline's skills to the test.