Darkness is not like Serendipity, and Nothing does not have the "Easy Focus" boon - in fact, she has no boons because she didn't take any drawbacks to her magic; she can in theory cast her darkness while bound and incapable of movement and really, in any condition so long as she's capable of taking a standard action at all, which of course, makes perfect thematic sense: she's a being made of darkness, detatching a portion of herself is very easy.
Nothing:
And where does it say I have to use an action to concentrate? That sounded weird to me so I looked it up and all I can find is that if I get hit (or otherwise distracted) whilst concentrating I have to roll to maintain it. I couldn't find anything about "You have to use your Standard Action to sustain it".
That's because it's not a "Sphere of Power" unique rule - it's just a normal Pathfinder rule: mantaining a spell through concentration requires a Standard action. Here's the link:
https://www.d20pfsrd.com/magic/
And here's the specific passage, which can be found under the "Duration" header:
quote:
Concentration
The spell lasts as long as you concentrate on it. Concentrating to maintain a spell is a standard action that does not provoke attacks of opportunity. Anything that could break your concentration when casting a spell can also break your concentration while you’re maintaining one, causing the spell to end. See concentration.
So, yeah, whenever a sphere ability says "you can mantain the effect with concentration, unless you pay X SP to make it last for (whatever time)", that means "if you don't pay for it, you're gonna be spending your Standard Action mantaining this effect". I can agree that it's not very clear, but those are the rules.