I have a question: What in the world is Shige's personality like? I only know she calls herself the cutest member in MM (which could very well be true
).
Hum..that's actually a hard question. Since Sayu's one of my favs, I'll try to take a stab at it.
Let's see Sayu does call herself the cutest member and she does believe it, in that those were the results of the utaban lie detector test. Hence she has a very narcissistic personality and has a great deal of confidence at times because of this. Though at the same time she's not big headed in that you can tell she's just using her cuteness to create a character for herself. While she says she's the cutest, she comments on how other members are so cute (like Reina) and that she can't beat the cuteness of babies and hamsters and that she's lucky that she grew up looking so nice because she considered herself ugly as a child
As for how other's view Sayu and her cuteness thing...Miki had commented on how Sayu has a dark side. This is in referrence to how Sayu is still into the cutesy stuff even though she knows she's getting too old for it among other things. She's also very conscious of the things she says (comment about being careful not to let others see her darkside and comment about hometown accent on radio show)
Sayu also seems well manned? She's always speaking in a polite way (except to Reina and Eri). It's like how she still addresses all her senpais by their last name. (Ie. she calls konkon Konno-san while others of her generation just call her konkon. Same goes for Yoshi and Miki. Surprisingly she even calls Risa Niigaki san -referrence to ep 259 or 260 where Sayu addressed Reina as Niigaki san over the phone by mistake)
Let's see what else...
Ah Sayu's also a boke (as shown on Music Fighters) but at the same time others in hello project have commented that she's actually pretty smart. She's also mature and reliable in that Risa commented on how she's a lot more mature than Eri (in which Sayu agreed) and she's reliable in that Eri commented in her futarigoto that she would depend on Sayu for the things she forgets. Plus on the xmas ep of Hello Morning even though Sayu seemed freaked out about the roller coasters she was still able to pull herself together enough to answer the questions (which was actually very surprising

)
hum...I can probably think of more to say but I think I should stop before this gets way too long. Hope that gives you a little insight on Sayu's personality even though some of it is a little confusing
