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Mecha tattoo artist, as the name suggests, is the one who carves patterns on mechas.
The tattoo master uses spiritual power to draw the 'formation', and then the mecha master uses spiritual power to trigger the 'formation', thereby gaining certain abilities, mostly attack abilities.
Possessing spiritual power is the most basic condition for becoming a mecha tattoo master.
It took Jin Ran three years to use his spiritual power to draw the most basic magnetic patterns.