|This build aims to make Shiro an absolute beast of a tank on the enemy phase.
For the IV's, +res or +def are the best for his boons as the goal is of course for him to tank as much damage as possible. Res is preferred as his base def is already pretty good. Hp is chosen as his boon because his weapon refine will make up for it, and he shouldn't be taking much damage anyways.
For his weapon we chose Berkut's Lance+ refined for res. The refine will help increase his res to be closer to his def, and the +7 when he is attacked pairs nicely with his native steady stance.
For his assist his native swap is an excellent option, as it allows him to get himself in a better position or get an ally out of a bad one. Reposition is another good option for getting his allies out of a bad situation.
His special should be either bonfire or ignis. Either one works well, which one you use really just depends on whether you want more damage or a shorter cooldown.
For his passives we go with steady stance for his A slot. This allows him to have even more def on enemy phase, and he comes with it naturally. Alternatively, a more expensive option could be steady breath, as the special charge bonus definitely outweighs the two less def he would get. For his B slot we go with quick riposte. This is the go to for enemy phase tanks like Shiro, allowing for guaranteed follow up attacks. For his C slot we go with def tactic. He comes with it naturally, making it a great option for him to provide some buffs to his team.
For the seal we choose fortress res. This combined with a res boon and weapon refine brings him up to 35/34 def and res respectively, a noticeable improvement over his 22 base res. This is brought even further on enemy phase with Berkut's Lance and steady stance to an excellent 41/41 defensive spread. Have an ally running res tactic C and def tactic SS and now he has 47/47 def and res on enemy phase. With this, very few units will be able to much damage to him at all.