This film is about the overflowing passion wreaking havoc because the artist does not exist in a vacuum.
The characters are a teenage visual artist, his friend, a talented poet, a religious girl who is passionate over the artist, and a fourth character who doesn't much talk - a flutist girl who is the object of fascination or obsession for the artist, although he never interacts with her.
So this becomes something of a love triangle or love quadrangle, if the object of the secret admiration of the artist can be considered an "angle" even though she is basically nothing more than a spectre in the plot rather than a whole character.
But this is essentially about emotions and as they relate to art. The artist has very poor emotional self-control, suddenly and apologetically venting his strong rage, his lust, and even his grief and regret to the detriment of all those around him. Rather than have a creative essence, it's more of a destructive one, and this is embodied by the portrait that he continuously works on throughout the film which he keeps changing completely from time to time.
This uncontrollable passion must unfortunately be suppressed, however, in regards to the object of his fascination, who he seems completely unable to approach. We're never quite sure whether this is because of some sort of artistic integrity, refusing to disturb his image of her, or because of some sort of cowardice or fear about the situation or his own feelings.
All of this ends up consuming and destroying those around him.
Beneath this main line is an undercurrent of hypocrisy or juxtaposition within the same beings. The artist who is always so passionate cannot consummate his passions for the object of his obsession; the poet so quiet, reserved, and even-tempered ends up being unable to deal with his emotions when faced with a true tragedy; and the Christian girl gives up all her ideals in an instant and doesn't ever seem to care that much about others in the first place.
Along these same lines, the spectacular cinematography should be mentioned. The film gives us scenes of a rural Japan bogged down by the heat of summer so effectively that you can feel the humidity in the air and the same goes for the biting Japanese winter. In one year there is such stark contrast, just like in every person there are massive, effectively inexplicable conflicts and hypocrisy.
Honourable Mentions: The Ballad of Narayama (1983) - Also very much a film about the stark sparseness of winter as much as it is about the human condition.
