Fridge Horror: The American soldier, "Sam", wounded by Colonel Nishi then brought in is clearly scared shitless. He would have no doubt heard stories (all of them true, unfortunately) of Japanese soldiers brutality towards POW's (or seen the results first-hand), but Freeze-Frame Bonus reveals he is also a flamethrower operator. In the Soviet-German and Japanese-American theatres, extraordinarily few flamethrower-men were ever taken prisoner.
He Really Can Act: Did you know Saigo is played by Kazunari Ninomiya of the boyband Arashi?
Nightmare Fuel: If you had nightmares from Flags of Our Fathers, you ain't seen nothing yet. The most horrific scene? Some of the Japanese soldiers commit suicide by holding their active grenades to their bodies. while you are almost yelling, "Idiots, your commander told you not to do this!"
The scene in which the captured Marine (possibly Iggy) is bayoneted repeatedly isn't any better.
Some Anvils Need to Be Dropped: War is bad, and the other side is human as well. This is shown when they read a captured Marine's letter from his mother.
The scene in which Shimizu and another Japanese POW are executed by two Marines simply because they don't feel like watching over them, and when Saigo finds their bodies.
The entire film, when it's not being horrifying and realistically depicting War Is Hell, has the air of inescapable tragedy as most of the main characters come to terms with their situation, mortality, and the ultimate futility of everything.
Near the ending where Saigo cried when General Kuribayashi committed suicide, after telling him that the section of Iwo Jima was still considered Japanese soil.
After Sam's death, when his mother's letter is read to the cave soldiers, reminding them that their enemy is as human as they are.