That definition very much describes the WORLD GOVERNMENT, which is a centralised, autocratic government headed by dictatorial leaders, and Akainu's role in it, which is the means by which said government violently suppresses opposition.
We don't need to know the specifics of Akainu's views; he serves an oppressive, authoritarian regime that enslaves and rules through violence, control of information, misinformation and extrajudicial killings - including that of civilian scholars and all those critical of or in contradiction to the state dogma, i.e. all those that can be considered a threat to "the group", which is what fascism boils down to.
Fascism boils down "This is the group. This is how we do things. Conform, or else."
Whether Akainu likes his superiors is irrelevant. Fascism cannot sustain itself precisely because it is an ideology that needs out-groups and enemies to ostracise to sustain itself. Infighting and collapse is the inevitable fate of all fascistic regimes. So, even if Akainu one day decided the Gorosei had to go and removed them from power, nothing would change his views on how to wield that power. He already believes Absolute Justice, which is a product of the World Government's influence, permits summary executions for dissent, desertion and insubordination - i.e. fascism.
I'll be charitable and chalk this up to genuine ignorance, rather than the blatant denial this reads as. Here's a video that breaks down what fascism actually is.
I would also generally recommend trying to form understandings of concepts from a historical context rather than attempting to get by on textbook definitions.