His former mentor was Hatohara. He was very fond of her, and praised her skills despite her lack of will to shoot people directly. After her apparent dismissal from Border, he refused to acknowledge anyone else as a mentor.
He is first seen sniping at a target during Sniper practice. He does not actually hit the target, but instead makes a star shape. Afterwards, Tōma explains that he is Ema's new mentor, but Ema denies this, stating that Hatohara was his only mentor. Chika, knowing of Hatohara's story, then begins a discussion about her with him. During this conversation, she accidentally gives away that she cannot shoot people either. Later, he is seen in Kageura Unit's base watching logs.
During the Rank Battle, he snipes at Ninomiya to cover for Kitazoe, but his shot is easily blocked. Ninomiya then goes to hunt the two down. While Inukai is pursuing Chika, he and Kageura defeat him together, but Ninomiya attacks Ema. Ninomiya asks why he was supporting Tamakoma Second, but Ema informs him that that was not the case, and that he simply despised Ninomiya Unit. He is forced into a building, where Ninomiya later defeats him.
After the Rank Battle, he does sniper training with Chika. Seeing how she resembled Hatohara in that they both considered themselves useless, he trains her by teaching her about Lead Bullet, and its combination with Sniper Triggers. He reveals, internally, that he did not want Chika to suffer as Hatohara did due to her perceived uselessness.