Sosuke Aizen's splash portrait (from the manga Bleach by Tite Kubo).At first glance, Aizen appears to be a rather nondescript character. While in the realm of manga, glasses are frequently shown as being "cool" or "trendy", his thick-rimmed glasses are an almost universal symbol of a soft-spoken intellectual; weak in both mind and body. His expression, too, is bland, though friendly. However, this portrait (published in the volume where he is established as the story's true antagonist), suggests that this impression is false.
Of note is the extreme contrast, which throws the blandness of his expression into an eerie light. His eyes lack color or reflection, giving him a very piercing gaze. Note, too, that his eyes aren't "smiling" - there's something sardonic, almost ironic in his demeanor. The seemingly kindly nerd is actually evil and dangerous, and has since discarded his mask. Finally, his name (written behind him in traditional brush strokes) is drawn very aggressively, even savagely; it's a very violent signature.
On "splash" (eyecatch) pages, it's not unusual in manga for the manga-ka (writer/artist) to do a picture of a character who figures heavily into the plot or story arc. Generally speaking, said portraits are of the character behaving in a characteristic manner - a shy character might take a more submissive, defensive pose, for instance. Aizen dominates his page, gazing down at the audience, serene and pitiless.

