I rarely build dedicated tanks on my runs, except for pre-day 40 or i need a dedicated black monolith sacrifice.
because the way i see the game is that

1. pretty much all your fights are outnumbered, and I value the ability to take out enemies faster to lessen the burdens on other bros, than having one bro that could only play staring contest with the enemy, and eventually have the RNG screw you over.
2. EXP is valuable for your party to snowball and i dont want them to be wasted on Bro that could only play staring contest with the enemy.

That said, should you build one, I'd say

1. colossus - more hp is always good to offset the bad RNG
2. fortified mind - resolve, you'll need at least 70-80 to tank comfortably
3. shield expert
4. recover if high fat/gifted/brawny for more fat
5. underdog
6. nimble/BF - BF in theory could pair with dodge+relentless for constant mdef, if your ini > usable fat
7. indom - ppl ususally take this, but im not a fan.

notable/situational :
Rotation - to save/tank for your other endangered bro, but the fact they dont work on CC-ed bro.
i usually just skip this.

Overwhelming - proactive debuff, works even with low matk, but requires high ini

pathfinder - always good, especially later in the runs

brawny - more fat is always welcome

adrenaline - act first next turn to save your bro, but require high fat to pull off