The answer of the seventeenth riddle - Sacrificed On Duty
The first paragraph.
Once in the darkest of times
The great man in the shadow of bad guy
The kind man who fought for justice all his life
Had sacrificed the most important thing
To prevented the said thing of another human being
From losing it away...
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» The scene had happened at night, and a man which was an undercover in the BO. The male ones we know are Akai-san, Ethan-san, Amuro-san, and Scotch-san. 'Sacrificed the most important thing' was a person's life, meant the man was already died, so that left Akai-san (Fake death), Ethan-san and Scotch-san in the choices. Two of them actually lost their lives to save another agent from being exposed and killed.
The second paragraph.
Another realized what he's going to do...
Trying to...
..Struggle, trying to stop...
But they had no choice...
As it was something he must do
...
So please...never give up...
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» There's someone trying to stop the man from doing something, and plus with the 'he must do' meant he was going to take his own life by himself and that another person was also on the scene.
And with that cleared, we can cross Scotch-san out, because we don't really know how exactly he died. The same with Akai-san because James-san, who could stop him wasn't at the scene (Raiha pass) at the time.
The Conclusion
In the Clash of Red and Black arc at episode 500 - Testament, there's a flashback to when Hondou Ethan made a scene to looked like his daughter, Hondou Hidemi/Kir killed him after realizing his identity as a CIA agent to protect her. He had said to her to 'never give up' and pressed the trigger of the gun in Hidemi's trembling hand.