Saori is convinced that something’s up with Minato, so she keeps after her son until he admits that he was physically attacked by his homeroom teacher, Mr. Hori (Eita Nagayama). Saori’s heard and seen enough to pursue Hori, and her reading of events is apparently confirmed by the insincere apologies she gets from him and the school’s reserved principal, Makiko Fushimi (Yuko Tanaka).

At this point, the plot of “Monster,” which was scripted by the celebrated TV writer Yuji Sakamoto, shifts focus to Hori’s perspective. As you might expect, Minato hasn’t told his mother the whole truth. Some school bullies are also involved, and so is Yori Hoshikawa (Hinata Hiiragi), as well as Yori’s withdrawn father (Shido Nakamura). There’s also obviously more to the principal’s seeming indifference and Hori’s defensive skittishness, though not enough to paint a tidy picture of either character. However, we learn more about what’s really going on with Minato and Yori, two close friends who live in their own semi-private fantasy world.

Based on this short synopsis, you might imagine that “Monster” is a sort of middle school “Mystic River” that inevitably casts a very broad sort of blame on yet another small community of blinkered loners. Thankfully, while “Monster” depends on dramatic irony and revelatory twists, it’s also a showcase for director Hirokazu Kore-eda, whose knack for collaboration brings out the best in his actors, especially his younger cast members. To better serve this story, Kore-eda (“Broker,” “Nobody Knows”) focuses on impressionistic, revealing details about Minato and his mom, as well as Fushimi and Hori.

Still, “Monster” isn’t really about who really did what or why. A lot is explained, and a few are implicated, but not everything and not everyone. Saori doesn’t become pigeonholed as a villain after we learn that she was wrong to attack both Hori and Fushimi without knowing the whole truth. And while Fushimi gives a kind speech at the end, her unyielding response to Saori’s desperate questions also doesn’t look much better in hindsight after we’ve gotten to know her better.

A nesting doll narrative like “Monster” seems to encourage viewers to cast their own judgment or maybe even share the impossible emotional burden of these characters. Who could have known, or really seen everything that happened, and why didn’t everybody respond better? However, what’s really striking about Kore-eda’s latest is his diligent attention to mood and a credible sort of subjective reality.