weakness & fears
Since Amaterasu is a god, her strength depends on people’s faith and their beliefs in a god, or gods. She does little things to restore people’s faith in the gods while venturing through Nippon and Issun, acting as her Celestial Envoy, helps do so during the tail end of the game. Without faith, she would probably find herself in a tight spot depending on who or what she is fighting against.
But even if she was at her weakest, Amaterasu would be unwilling to sacrifice anyone for a cause. She would much rather put herself in the way of danger and get hurt or killed, herself, if it meant being able to save a person. Shiranui had sacrificed himself to help seal away the great demon Orochi and protect Nippon and Amaterasu would do the same, if she ever has to. It is why she puts herself out in harms way to protect people from the threat of demons or those who would wish harm on others.
Yet, despite that, Amaterasu is benevolent and sometimes her kindness can cause harm. An example of this is when she helped out Ninetails, who had taken on the appearance of the priestess Rao, and retrieved the Fox Rods from the Water Dragon. With the rods Ninetails had been able to break Queen Himiko’s barrier and kill her. However, it was a sacrifice that needed to be made (and, as Waka pointed out, something that even Amaterasu knew). She also wound up helping out Orochi’s chef, in the Moon Cave, by getting him the ingredients he needed for his meal to be completed.
Though not quite as important as faith or the above, Amaterasu is a glutton and can be found on the lazy side. She’ll flop down in the middle of someone’s long winded explanation and doze off or may take to eating instead of doing something else. She is also rather hard headed and stubborn, depending. She also hates to lose battles or a race (which is, quite possibly, one of her biggest peeves). The fear of losing stems from the fact that, if she does lose against anyone (especially Yami) then it could very well mean the end of Nippon - or the end of the world; a world without the sun, a world covered in darkness, is one thing that sends an absolute chill through her body.
She can’t swim, either, for some odd reason and she is not a big fan of water in the least. So getting her to take baths or to go swimming will be quite the task (especially the former).
Amaterasu, while having a voice of her own, also does not speak, as she has grown quite used to having others talk for her. This could be considered a weakness since most people are used to vocally communicating with one another and may be unable to reach what she is trying to get across through actions and body language.
Also: breasts. Though it may be thanks to Issun’s influence she honestly just cannot help but find herself staring at them if they’re a bit on the large side and...right there. In her field of view.