Min/Max Boards

I am currently designing a campaign (it is not based on the type moon series) and I want to use a character that has always fascinated me.

As good lords of the dungeon that we are here, we know the armors and stealth combine as much as milk and lemon, I wanted to know if they had some ideas ...

Currently I have it designed as a swordsage with a few levels of warrior.

But he needs more.

If anyone knows the story of the character (based on the history of FGO) the build it is very low power, he is the instakiller, the assassin king.

If someone here plays the saga or knows what he is talking about, I would like to hear ideas on how to create this mass of force with armor but even being a furtive character

Thanks so much.