It is a meme in Japanese BBS forums, where the face \(^o^)/ is generally associated with the words 'Owataaaa~' Which means 'It's the end~', which, depending on the situation, means 'Death is imminent and un-avoidable~' or 'This is nearly finished~'
So, the artist could be making a statement that he has nearly finished this time consuming drawing.
Hiding a blushProudEnlightenmentThank you for your work.AngryMiserableSulkingBustedHaaaHappyflabbergasted ExpressionActing strongBitterDespairSurpriseAnticipationPainedCryingTroubledDisdainSchemingSneeringBewilderedDidn't knowSleepyShockConfessingThe Rampaging HawkThe Slithering SnakeSparkle ☆Uho-ho-ho~ComplexMovedWhy?SmilingIn a spot [of trouble]Tense