Tatsuya Kuruma captains the B-rank Suzunari First squad within Border. Hailing from a wealthy family that financially supported the organization and donated the Suzunari Branch building, he retained approachability and humility despite his affluent status.

He presents as a light-skinned, slender young man of average height. Medium-length, wavy light brown hair frames his face, distinguished by black eyes featuring slit irises. His typical attire includes collared cardigans or sweaters layered over simpler shirts, while his standard Border uniform consists of a forest green shrug jacket with black stripes, a black shirt featuring green vertical lines, beige pants, and knee-high brown boots.

Kuruma's personality radiates exceptional kindness, consideration, and an almost impossible capacity for forgiveness, naturally drawing others to him. He displayed this forgiving nature profoundly when teammate Taichi Betsuyaku accidentally boiled all his tropical fish; despite his grief, Kuruma harbored no anger and forgave the incident immediately. His altruism drove him to cycle through rain solely to meet Tetsuji Arafune, aiming to alleviate Kō Murakami's guilt over Arafune's class change. He recorded a video with Arafune to reassure Murakami, demonstrating consistent support for those around him.

Initially timid in combat, Kuruma displayed visible anxiety during Aftokrator's large-scale invasion while his squad suppressed Trion Warriors, requiring reassurance when confronting a Rabbit. Designated as bait in a trap against the powerful Neighbor Lamvanein orchestrated by Haruaki Azuma, Kuruma felt genuine terror. Yet, his coordination of Shields contributed to Lamvanein's defeat, earning Suzunari First an Excellent Distinguished Service award. Observers like Kei Tachikawa noted a significant shift in his combat demeanor afterward, as he displayed increased steadiness in subsequent rank battles.

His tactical growth became evident during B-rank wars. Against Nasu Squad and Tamakoma Second, Kuruma demonstrated improved battlefield resolve, coordinating with Betsuyaku to engage Rei Nasu directly and persisting under heavy fire despite injuries. Left alone against Nasu after his squad's defeat, he executed a last-ditch Hound attack exploiting her blind spot, eliminating her despite bailing out himself. His adaptability continued as he and Murakami developed a specialized mid-range combat formation enhancing their firepower. They later employed environmental tactics like manipulating mall lighting against Kageura Squad and Azuma Squad, showcasing Kuruma's evolving strategic mindset.

His leadership extends beyond tactics. He maintains a supportive dynamic within Suzunari First, often calming tensions caused by Betsuyaku's clumsiness or mediating external pressures, such as defending Murakami from Tachikawa's criticisms by interpreting them as signs of esteem. During the Galopoula incursion, he operated within a unit of close and mid-ranged fighters, contributing to the defense against Idra Trion Warriors and later coordinating with senior agents like Reiji Kizaki, emphasizing rear-guard protection and squad cohesion under centralized command.

Outside combat, Kuruma enjoys aquaria and macaroni gratin, favoring tomato-flavored instant noodles though he often yields them to Betsuyaku. He possesses notable luck, being one of the few unaffected by Nozomi Kako's fried rice. The author likened his personality to Yūta Miura's, humorously noting Miura lacked his wealth, and referenced his curly hair in relation to his Buddha-like kindness.