The answer of the seventh riddle - Fallen Angel
Here comes, to the Fast and Short style again!
- The first line "An angel who had fallen into the hands of merciless devils"
The keyword are 'Angel' and 'Merciless devils'
Three person we knew as 'Angel' are Ran, Ai/Shiho and Miyano Elena(Shiho's mother...Akemi's too)
Ran has nothing to do with 'devil' (well...not yet anyway.) so it's Ai-chan or Elena-san, as both were in the BO that is 'Devils'
- The second line "To the hell where no light couldn't be seen"
This expanded where this person were in, as BO is like a hell on earth. (On-Surface meaning)
Some might already figured it out since this line, but I'm going to explain this in basic thoughts first, before we go in deeper speculation. As we all know this line actually indicated to her nickname 'Hell's angel' (Actual meaning)
- The third line "And separated from her children since they were young"
Well, this line was an obvious give away, that Elena-san was only one(female) person in BO we know that has children (Read: RainbowKittyRune's review).
- The fourth line "Only her voice she could passed onto"
And
- The fifth line "Her oldest child, who she hoped could help her younger child"
The four tapes she gave to Akemi, so that she could passed them to Shiho, and that Shiho could open and listen to them on her birthday.
- The sixth line "...For them to have a better, peaceful life..."
As she wished they would escape from BO and have a normal, better life.
- The seventh line "Telling them she loved them"
Exactly what it meant...
- The eighth line "Before she was gone, never to be seen again"
She died(along with her husband, Atsushi)on what they told Shiho as an 'accident'.
The answer was Miyano Elena, The Hell's angel, The Mother of Miyano Shiho and Miyano Akemi, and the wife of Miyano Atsushi, The Mad Scientist.
I gave you a short, simple explanation because I know you people don't even bother on actually reading this anyway...
Let's waste no time as I fly off in a distance...with my beautiful, gorgeous wings...? XD