In Demon Slayer: Kimetsu no Yaiba and the other action-fantasy anime/manga, romance is generally a side issue to the real story. Whether there is a love interest or not, it could make a difference in explaining the emotional evolution or human side of the character.
Sometimes in the middle of such intense action, with brilliant supernatural evils, and tragic pasts, romance could be an anchor—a very quiet constant amidst chaos. This makes even more sense to boys, such as in Demon Slayer, where emotional relationships help balance those deep responsibilities of loss and perseverance in other themes.
Demon Slayer does provide a tender love interest for the main character, Kamado Tanjiro. It develops little by little in the storyline without taking attention from the center of the narrative.
The relationship between the demon slayers gradually progresses in the series with Kanao Tsuyuri. Most of their love goes unmentioned in the events taken up by the main storyline, but the epilogue's scenes show that it definitely goes on to mature into a romantic one. This adds an emotional layer to his journey, meaning that even in the course of a suffering life, love and normalcy are within the reach of attainment.

From the beginning, a warm-hearted Tanjiro has been depicted to be devotedly passionate toward his sister, Nezuko, and weighed down by his entrance into the Demon Slayer Corps, a tragedy of selflessness planned around his character.
Such parameters create his identity, leaving little room for traditional romance in the early chapters. But he and Kanao are slowly beginning to broach something more. Their moments are few and far between; gestures that mean so much more than shouting declarations. Kanao's emotional restraint contrasts with how Tanjiro seems completely free with everyone, which adds fuel to the slow-burning kind of relationship that develops throughout the series.

All of these elements contribute to the pace of their relationship. Because she was brought in under very strict conditions of emotional restraint, she uses a coin toss to make decisions. Tanjiro has helped Kanao think and feel independently. Tanjiro, in one of the most pivotal moments of their relationship, encourages Kanao to follow her heart rather than chance, marking an important emotional turning point for both characters.
As we come closer to the end, we see that the bond between Tanjiro and Kanao tightens further, especially during and after the fight against Muzan Kibutsuji. Why Kanao would risk her neck to rescue him after he transformed into a demon for a brief period, using the last bit of serum that would have saved her own life, is not particularly romantic. But it does show just how deep her feelings run.
Even if Tanjiro never replies in words within the main timeline of the manga, it is quite evident through his actions and thoughts that he feels gratitude and concern towards Kanao.
Tanjiro’s Romantic Future in the Demon Slayer Manga
Once again, set generations into the future, in the post-epilogue of Demon Slayer, the readers are introduced to the modern-day descendants of several main characters. It is heavily implied - and widely accepted - that Sumihiko Kamado and Kanata Kamado are the descendants of Tanjiro and Kanao. These characters not only resemble their ancestors physically but also in their personalities. Thus, it is confirmed that Tanjiro and Kanao would finally settle down into a life together after their era ended.
Of course, the anime is going to be just as subtle in its romantic evolution as the manga has been. The anime has yet to reach the epilogue content, but fans can expect that portion to finally surface in the last seasons or films. Their quiet relationship, however, seals the endings of both arcs rather well, suggesting healing, peace, and a resuming into ordinary life.
In addition to achieving emotional closure, their romance also emphasizes one of the quiet demon-slaying themes: the hope of peace beyond the suffering. Both Tanjiro and Kanao lose families, undergo horrific battles, and have to bear immeasurable burdens. That they can find happiness together brings a ray of hope beyond the battlefield. Their love story is quietly victorious in acknowledging the humanity that still exists through the horrors of war.
Demon Slayer portrays Tanjiro Kamado as having a love interest. It might be a subdued relationship with Kanao Tsuyuri, but it effectively sets the standard in terms of the emotional topography of the series.
In this case, with all that the anime and manga portray about demon slaying-or-anything-but-fight-battle and deep dives into personal conflicts, even the pale tinge of love has great and meaningful closure to Tanjiro's story. For even within a world full of darkness, kindness and connections ensue.