3 ideas
Each volume places technical content inside a comic story with recurring characters and a motivating problem, while a subject expert separately checks that the mathematics is correct. The division of labour lets the story carry motivation and pacing, and the expert's review keeps the rigor intact. The accessible form does not dilute the content.
The protagonist is a novice with a concrete personal stake in the subject, such as needing to manage a failing business or pass an exam. The character voices the confusions a real reader would have, and a tutor figure resolves them in dialogue. Following the character's struggle gives the reader permission to be confused and models the path from confusion to competence.
Technical ideas are introduced through a specific situation the reader can picture before any formal definition or notation appears, such as tabulating a kingdom's fruit orders before explaining relational tables. The formalism is then presented as a tidy description of something the reader already understands. Formulas answer a question the reader already has instead of being memorized cold.