Light Novel I'M GOING TO GROW A "CASTLE" ~ THAT CUTE LITTLE GIRL WANTS TO BECOME AN INVINCIBLE FORTRESS ~ Famitsu Bunko

Product description ※Please note that product information is not in full comprehensive meaning because of the machine translation.

Thoma, a D-class adventurer, is rescued by a mysterious little girl, イェタ, who is dying, but she lives in an abandoned castle and is the spirit of that castle! Moreover, if she is offered a demon, she can renovate the castle and arrange luxurious facilities. After hearing イェタ's wish to become a "splendid castle!" Thoma lives with her, and as she struggles to power up the castle, she deepens her bond. And -- "Yay! The castle has become strong again!" That cute little girl (castle) begins a carefree and nurturing life.