First you need the kikumonji sword.
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the best will be the fatalis armor black or white best defense. also you can combine the akantor & ratalos armor
first of all get kushala armor then a dragon element blade and atttack its horns or go to youtube and type in lunastra guide.
You can't be invincible, but with the right armor and items you can get pretty close. You just need to try combinations. Being invincible would just be cheating though.
There is no way to "trim" armor. You can only get trimmed armor as a monster drop or through the Treasure Trails minigame. Anyone who says they can "trim" armor is lying. Don't listen to them.
o81