An Adventurer's Daily Grind at Age 29 follows Hajime Shinonome, a 29-year-old silver-ranked adventurer living in the village of Komai. Having grown up in a slum and experienced severe hunger, he has come to appreciate his stable life, taking on quests and hunting for food in the local dungeon. During a routine expedition, he discovers a young girl named Rirui who has been abandoned by her parents and is about to be eaten by a slime monster. Remembering his own difficult past, Hajime decides to rescue and care for her.

The story is set in a fantasy world where adventurers of various ranks take on quests to protect villages and explore dungeons. The narrative focuses on the daily life of Hajime as he navigates his new responsibilities as a guardian. Rirui, who initially has nowhere else to go, soon begins training to become an adventurer herself. As she adapts to village life, she reveals unexpected abilities, including a transformation into an adult form at night, which eventually leads to the revelation that she belongs to the ancient succubus species.

The main cast includes Hajime, a skilled adventurer who is well-regarded by the villagers but struggles with past trauma and avoids forming deep attachments; Rirui, a spirited orphan who is determined to become useful; Olive Carmen, the elf who heads the local guild branch; Veronica, a succubus who runs a shop and has known Hajime for a long time; Anyango, a young dwarf girl who becomes Rirui's friend and adventuring companion; and Cocko, the daughter of a chicken beastkin researcher who also joins the group. Other notable characters include Sekihime, a medusa known as the Dungeon Destroyer who develops a crush on Hajime due to his kind treatment of her.

Notable narrative arcs include the initial rescue and adoption of Rirui, as Hajime and the guild struggle to determine her origins and place in the village. Another significant arc follows Rirui as she trains to become an adventurer, forming a party with Anyango and Cocko to tackle low-level quests. The series also explores Hajime's past as a slum orphan and how it shapes his relationship with Rirui, as well as the slow development of his connections with the other villagers who see him as their protector. The anime adaptation, which aired for 12 episodes, follows these daily adventures and the growing bonds between Hajime and the people he has come to care for despite his initial reluctance.