Been trying to reckon this build for a bit. For the folks who don't recognize the source, it's an anime where the main character creates a video game character with all defense and proceeds to break the game with all sorts of weird finds and combos.

So the goal here is to find weird ways to get into as much AC as humanly possible. And the side goal: weird flexibility. In the show, most of her attacks are ranged

I think the base has to be forge cleric 6. If we find our way into plate, that's 22 AC.

If we ignore phb+1, the obvious 2nd class is an armorer artificer, which can build up +2 AC immediately and access another +2 AC in "magic" items over 14 levels. That does get you a good amount of weird too and matches the show in a number of ways. 

If we keep phb+1 I've been leaning towards divine soul sorcerer. Hear me out: shield spell and two spellbooks to choose from for all of the utility we could ever need.

There are other options to look into: dipping warlock would add some poisons spells, fighter can add more ac, paladin could add defensive maneuvers.

Thoughts?

What's phb+1?

If you're only focused on AC, not saves, an obvious choice for race is warforged, for +1 to AC while wearing armor.  Don't forget, a single level of Fighter also grants +1 to AC in armor.

In terms of classes, your math on Artificers is off.  An L14 Artificer can easily be wearing +2 plate (enhanced defense, L2+L10), a +1 shield (repulsion shield, L6), a +1 cloak (cloak of protection, L10), and a +1 ring (ring of protection, L14), for AC 25 base, before stacking with warforged or L6 forge cleric (L1 forge cleric won't stack with infusing armor).  If you're assuming no one has access to magic items unless their class gives it to them, I think no one can beat a pure Artificer for AC if they're also pure.

For multiclass AC, you should be able to make a Bladesinger 4/Monk (or Barbarian) 4/Fighter (or Rogue) 12 go higher - that build reaches AC 25 just from Int 20 Dex 20 Wis (or Con) 20, but because Bladesinging won't stack with shields and Monk/Barbarian naked armor won't stack with armor (or mage armor), I think going any higher would require feats, like Dual Wielder. 

I'm not sure offhand which of these builds would win the AC race, since of course the Artificer can also take feats (and can multiclass).  It's just that Fighter and Rogue provide extra feats to work with.

phb +1 refers to the AL rule of phb+1 extra sourcebook

Quote from quindraco >>

What's phb+1?

If you're only focused on AC, not saves, an obvious choice for race is warforged, for +1 to AC while wearing armor.  Don't forget, a single level of Fighter also grants +1 to AC in armor.

In terms of classes, your math on Artificers is off.  An L14 Artificer can easily be wearing +2 plate (enhanced defense, L2+L10), a +1 shield (repulsion shield, L6), a +1 cloak (cloak of protection, L10), and a +1 ring (ring of protection, L14), for AC 25 base, before stacking with warforged or L6 forge cleric (L1 forge cleric won't stack with infusing armor).  If you're assuming no one has access to magic items unless their class gives it to them, I think no one can beat a pure Artificer for AC if they're also pure.

For multiclass AC, you should be able to make a Bladesinger 4/Monk (or Barbarian) 4/Fighter (or Rogue) 12 go higher - that build reaches AC 25 just from Int 20 Dex 20 Wis (or Con) 20, but because Bladesinging won't stack with shields and Monk/Barbarian naked armor won't stack with armor (or mage armor), I think going any higher would require feats, like Dual Wielder. 

I'm not sure offhand which of these builds would win the AC race, since of course the Artificer can also take feats (and can multiclass).  It's just that Fighter and Rogue provide extra feats to work with.

Yeah, going by the show, saves are not a thing. If I wanted to be even more show-accurate, I'd find a way to drop my speed slower 🤣. This character doesn't get out of the way of things. Collecting resistances would be the bigger deal.

I wanted to avoid Eberron content as it's intended for a FR campaign, so I didn't include the warforged as a race option.

Re: artificer - I missed the level 10 artificer +1. Good catch. A forge Cleric 6/Armorer Artificer 14 would have a built in 27 AC before feats and magic items are added.

On the other side, I think following PHB+1 proscribed by AL is fun. Makes building more challenging and less game-breaking.

Forge Cleric + Divine Soul Sorcerer can get 27 AC (with 1500GP plate and the Shield spell) by level 7. BM Fighter 4 does add in another +1 AC for a fighting style and a maneuver with Bait & Switch for 1d8 AC. Gets us up to 28 AC at level 8 and potentially over 30 by level 11 at the cost of having angel wings at level 20. But how many campaigns make it to level 20 anyway? 😂

e: Could also take feats to get that +1 AC fighting style and the superiority dice move. The fighting style requires Tasha's as the +1

What's PHB+1?

Quote from quindraco >>

What's PHB+1?

 i already put a message on that, AL rules that you get players handbook and 1 other sourcebook to make a character

Quote from TabaxiRogueFighterClericWarlock >>

Quote from quindraco >>

What's PHB+1?

 i already put a message on that, AL rules that you get players handbook and 1 other sourcebook to make a character

Wild, right? I thought this was a pretty common thing :-o

You mean, everyone else is bringing these ridiculous character combos to the table?

i don't use the AL rules, i just know them. then again most of my players are pretty new so they don't know how to do crazy combos

Quote from TabaxiRogueFighterClericWarlock >>

Quote from quindraco >>

What's PHB+1?

 i already put a message on that, AL rules that you get players handbook and 1 other sourcebook to make a character

 Oh, thank you, I missed your answer.

Quote from kayakyakr >>

Wild, right? I thought this was a pretty common thing :-o

You mean, everyone else is bringing these ridiculous character combos to the table?

In general, my GMs usually rule something like, "No UA, no Wildemount, no third party."  (This is just an example.)  I don't engage in AL, and I've never before encountered the concept of being forced to choose between, say, Xanathar's, Mordenkainen's, and Tasha's, due to only being allowed 1 splat.

with my table any non-location(wildmount, eberron) based sourcebook is legal and UA and location based books are allowed if you ask the dm for approval

Quote from TabaxiRogueFighterClericWarlock >>

with my table any non-location(wildmount, eberron) based sourcebook is legal and UA and location based books are allowed if you ask the dm for approval

Right.  That sounds very normal (and reasonable) to me.

I would do Bladesinger + Artificer. You only really need to max INT and DEX, and take two levels of BS. With studded leather armor +2 (enhanced defense), cloak of protection, ring of protection, and shield, that's 21 passive AC (22 with warforged), 26 with bladesong, and 31 with shield.

Bladesinger/Artificers are particularly good with Battlesmith and Artillerist.

you can have a 40+ AC build, although many magic items are needed.

warforged bladesinger 2 / fighter 1 / cleric 1. only 4 levels needed

adamantine plate for 18 base AC, and immunity to crits. then, have enough tomes of clear thought so you have 30 int. blasesong let's you add your int modifier to your armor class, so that's 28. then, fighter defense fighting style gives you + 1 AC for 29. hold a shield, +3 for 34. then, wear 3 cloaks of protection for 37. then, warforged gives you +1 AC for 38. then cast shield of faith for 40 AC. last but not least, you can use your reaction to cast shield to increase your AC to an insane 45.

now, you can have more AC then that, but with the above build you are also immune to crits, so it's literally impossible to be hit by attacks.

Quote from HomebrewMindFlayer >>

you can have a 40+ AC build, although many magic items are needed.

warforged bladesinger 2 / fighter 1 / cleric 1. only 4 levels needed

adamantine plate for 18 base AC, and immunity to crits. then, have enough tomes of clear thought so you have 30 int. blasesong let's you add your int modifier to your armor class, so that's 28. then, fighter defense fighting style gives you + 1 AC for 29. hold a shield, +3 for 34. then, wear 3 cloaks of protection for 37. then, warforged gives you +1 AC for 38. then cast shield of faith for 40 AC. last but not least, you can use your reaction to cast shield to increase your AC to an insane 45.

now, you can have more AC then that, but with the above build you are also immune to crits, so it's literally impossible to be hit by attacks.

 Bladesong doesn't work with heavy armor or shields, and magic items with the same name don't stack (cloak of protection).

Quote from Thauraeln_The_Bold >>

Quote from HomebrewMindFlayer >>

you can have a 40+ AC build, although many magic items are needed.

warforged bladesinger 2 / fighter 1 / cleric 1. only 4 levels needed

adamantine plate for 18 base AC, and immunity to crits. then, have enough tomes of clear thought so you have 30 int. blasesong let's you add your int modifier to your armor class, so that's 28. then, fighter defense fighting style gives you + 1 AC for 29. hold a shield, +3 for 34. then, wear 3 cloaks of protection for 37. then, warforged gives you +1 AC for 38. then cast shield of faith for 40 AC. last but not least, you can use your reaction to cast shield to increase your AC to an insane 45.

now, you can have more AC then that, but with the above build you are also immune to crits, so it's literally impossible to be hit by attacks.

 Bladesong doesn't work with heavy armor or shields, and magic items with the same name don't stack (cloak of protection).

 cmon!!! well then go barbarian with 30 con and str (from manuals of bodily health and gainful exercise), for a base 30. add balsesong for 40. a ring of prot and 1 cloak of prot for 42. warforged for 43, shield of faith for 45, and reaction shield for 50. more AC, but you can still be hit by crits...

Quote from HomebrewMindFlayer >>

Quote from Thauraeln_The_Bold >>

Quote from HomebrewMindFlayer >>

you can have a 40+ AC build, although many magic items are needed.

warforged bladesinger 2 / fighter 1 / cleric 1. only 4 levels needed

adamantine plate for 18 base AC, and immunity to crits. then, have enough tomes of clear thought so you have 30 int. blasesong let's you add your int modifier to your armor class, so that's 28. then, fighter defense fighting style gives you + 1 AC for 29. hold a shield, +3 for 34. then, wear 3 cloaks of protection for 37. then, warforged gives you +1 AC for 38. then cast shield of faith for 40 AC. last but not least, you can use your reaction to cast shield to increase your AC to an insane 45.

now, you can have more AC then that, but with the above build you are also immune to crits, so it's literally impossible to be hit by attacks.

 Bladesong doesn't work with heavy armor or shields, and magic items with the same name don't stack (cloak of protection).

 cmon!!! well then go barbarian with 30 con and str (from manuals of bodily health and gainful exercise), for a base 30. add balsesong for 40. a ring of prot and 1 cloak of prot for 42. warforged for 43, shield of faith for 45, and reaction shield for 50. more AC, but you can still be hit by crits...

 You can't cast spells while you're raging, and bracers of defense would be better than the ring. Also, no one is going to get 15 different tomes. Plus, this build's fatal weakness... hold person.

Quote from HomebrewMindFlayer >>

Quote from Thauraeln_The_Bold >>

Quote from HomebrewMindFlayer >>

you can have a 40+ AC build, although many magic items are needed.

warforged bladesinger 2 / fighter 1 / cleric 1. only 4 levels needed

adamantine plate for 18 base AC, and immunity to crits. then, have enough tomes of clear thought so you have 30 int. blasesong let's you add your int modifier to your armor class, so that's 28. then, fighter defense fighting style gives you + 1 AC for 29. hold a shield, +3 for 34. then, wear 3 cloaks of protection for 37. then, warforged gives you +1 AC for 38. then cast shield of faith for 40 AC. last but not least, you can use your reaction to cast shield to increase your AC to an insane 45.

now, you can have more AC then that, but with the above build you are also immune to crits, so it's literally impossible to be hit by attacks.

 Bladesong doesn't work with heavy armor or shields, and magic items with the same name don't stack (cloak of protection).

 cmon!!! well then go barbarian with 30 con and str (from manuals of bodily health and gainful exercise), for a base 30. add balsesong for 40. a ring of prot and 1 cloak of prot for 42. warforged for 43, shield of faith for 45, and reaction shield for 50. more AC, but you can still be hit by crits...

Adamantine Plate doesn't make you immune to being hit on a natural 20 for the same reason Champions don't automatically hit on a 19.  You're conflating two distinct rules.  Critical hits do double (rolled) damage - they don't automatically hit.  Automatic hits don't do double (rolled) damage.  They're just distinct rules.

Also, Barbarian AC is DEX+CON, not CON+STR.  You need to be CON 30 DEX 30 INT 30 (or WIS 30 DEX 30 INT 30 if you do this with monk) to be base AC 30, 40 with Bladesong up.

Finally, you don't need multiple magic books - warforged don't age.  Just wait for your books to refresh.

The thing about Maple is that she doesn't actually have a high AC by D&D standards, she's just got a massive HP pool and takes tiny amounts of damage per attack if she's not outright immune to the damage type.