"The Elder Sister-like One" centers on the relationship between two main characters: a young man named Yuuto and his childhood friend, Akiho, who is several years older than him. Akiho has always played a protective, nurturing role in Yuuto's life, acting as a pseudo-elder sister figure. The story explores their evolving dynamic as Yuuto grows older and begins to see Akiho in a new light, complicating their once-simple bond.

The narrative begins with Yuuto reflecting on his childhood, where Akiho was a constant presence, guiding and supporting him through various challenges. Her caring nature and maturity made her a pillar of stability in his life. However, as Yuuto enters adolescence, his feelings for Akiho start to shift from familial affection to romantic attraction. This change creates tension, as Akiho struggles to reconcile her role as a caretaker with Yuuto's growing desire for a deeper, more intimate connection.

Akiho, for her part, remains deeply devoted to Yuuto but is hesitant to acknowledge his feelings, fearing it might disrupt their relationship. Her internal conflict is a central theme, as she grapples with her own emotions and the societal expectations surrounding their age difference. The story delves into their interactions, blending moments of warmth and nostalgia with the awkwardness and uncertainty of their changing relationship.

Supporting characters, such as friends and family members, occasionally provide perspective or add layers to the narrative, but the focus remains firmly on Yuuto and Akiho. The manga balances lighthearted, slice-of-life moments with more introspective scenes, capturing the complexity of their bond. Themes of love, maturity, and the passage of time are woven throughout, as the characters navigate the challenges of growing up and redefining their connection. The story avoids melodrama, instead opting for a grounded, heartfelt exploration of human relationships.