Masaru Tōno is a classmate of the esper trio The Children and childhood friend of Chisato Hanai. The organization B.A.B.E.L. secretly monitors their relationship, a measure requested by The Children and Fujiko Tsubomi with approval from the Japanese Cabinet.

He harbors a distinct dislike for espers, a trait significantly shaping his interactions. His relationship with Chisato became strained following the awakening of her telepathic abilities, when she inadvertently glimpsed his private feelings. This tension eased after both he and Chisato befriended Kaoru Akashi, paving the way for their reconciliation. Their bond deepened further over time, influenced by The Children acting as figurative "cupids."

Masaru's name draws inspiration from Tō no Chūjō, Hikaru Genji's best friend in *The Tale of Genji*. His given name, Masaru (将), carries meanings including "leader," "commander," "general," "admiral," "or," "again," "soon," "from now on," or "just about." His surname, Tōno (東野), combines "east" (東) and "field" or "wilderness" (野).