Hakuno was an NPC generated by the Moon Cell.
Based on a cryogenically frozen human Hakuno had no memory or sense of self though her human counterpart was a resident of Japan who suffered from Amnesia Syndrome and was frozen to await treatment due to the death of Twice H. Pieceman. She is still in stasis as of Hakuno's participation in the Moon Holy Grail War.
After being created in SE.RA.PH as an NPC, Hakuno like Twice, somehow gained self-awareness but unlike Twice she did not regain any memory of a "previous life" due to the fact that the original was an amnesiac to begin with. However believing herself to be a normal human Hakuno unknowingly took over the position of another participant who had died in the preliminary selection for the war. As an NPC rather than a human, Hakuno cannot enter the Moon Cell without being deleted as invalid data like Twice yet the Moon Cell requires more time to process the contradiction caused by the existence of the frozen body in the real world and so she is not instantly deleted and has enough time to make a wish.
Hakuno is initially lost over as to what she should be doing in the Holy Grail War and so her resolve to fight is lacking because she doesn't know what she wishes to accomplish, since the Grail is won by individual motivation, but they lack the core of motivation itself to claim it so that makes for a large handicap without the drive to win. Hakunon is neither someone who fights out of obligation like a soldier, or even someone strong-willed who always fights with their eyes on the prize in front of them. That is a great weakness and even if her Servant had the greatest Noble Phantasm said Servant would still lose to someone with that drive and not knowing that she was inadvertently entered in the Holy Grail War she cannot imagine that her reasons to fight was not very strong in the first place to have been cast aside so easily.
Hakunon knows nothing of the Grail War, and even one round in, she still lacks knowledge of even important concepts like Noble Phantasms and it is repeatedly pointed out by others that Hakunon is rather dense and sometimes fails to understand basic things especially ones related to a magus making her look like a rather hopeless Master among a crowd of talented Masters.
Though later, Hakunon does come to acknowledge and appreciate her allies, and can become visibly worried if something happens to Rin/Rani or their Servant.
According to Dan Blackmore, Hakunon starts out at the beginning of the War as an inexperienced and "green" Master, easily frightened by the other Masters such as Julius. This changes over time as she becomes more and more determined to not let the lives lost during the War to become meaningless.
In Fate/EXTELLA, as the ruler of SE.RA.PH, Hakunon demonstrates a serious and level-headed calm to situations, though can be surprised and shocked by certain situations like any other. This kingly aptitude has earned her loyalty of other Servants - including former enemies she fought in the Grail War such as Gawain and Li Shuwen.
Notes: Though the name given is more of a default nickname it's kinda a way how one can tell the difference between the versions of the main character or something like that, so I'll be going with this.
