Perhaps she is THE most versatile actress by a mile in the 97-2000 age group? Maybe she isn't a virtuoso, hyper-technically-gifted actress, but her applicable range of roles is incredibly wide (especially for someone so young like her). Think something from that bloke in Channel no Sonomama to outright creepy in Kasane, which is quite a feat.
Honestly I won't call actors who've won awards back to back and got nominated everywhere all the time underrated. The only 'legitimate' underrated actors in the list are only Ohgo, Tanimura, Taiga, Ikewaki, Aso Kumiko (relative to the likes of same age group big stars like late Kanno Miho, Matsu Takako, Miki Nakatani etc) and perhaps Ikematsu.
"Very complex character that I imagine most young actress would fail to portray."
I'd disagree. While Elaiza has proven herself as competent actress (well she deserves major breakthrough even IMO), many of her contemporaries at roughly similar age group (1995-1998-liners) are no less skilled and would do well in such character.
Japanese created the best Horror movies, like always!!
Not really. Since 2005 they've forgotten how to make good horrors and yet to rediscover it. Of course there are decent horrors made after that period appeared here and there but almost all of them are low-key.
2 
I'd disagree. While Elaiza has proven herself as competent actress (well she deserves major breakthrough even IMO), many of her contemporaries at roughly similar age group (1995-1998-liners) are no less skilled and would do well in such character.