Ok here's my entry for Fairy Tail Wizards, it's a build/guide that I have already tried and it works like a charm, sorry for the text wall.
Build to Erza Scarlet.
Synthesist Summoner:
This archetype is so much worse than vanilla summoner for two reasons:
Action Economy, unlike a normal summoner who can have up to two full round actions per turn the synthesist is no better than any other medium progression class.
Of course once you get split forms this is not an issue… at least for a limited time.
Weaker Eidolon your eidolon effectively loses skills and feats effectively limiting you to an average martial character without bonus feats and moderate BA that scales one level earlier than normal.
The advantages on the other hand is that MAD is so much easier to handle as a synthesist and effectively you can be quite a beast at higher levels although not optimal as other casters can be.
Class Abilities:
Fused Eidolon: This ability is the basis for this build, as it says “The synthesist wears the eidolon like translucent, living armour” ‘nough said.
Fused Link: This is the ability that Erza used during Pandemonium, damaging herself to keep on “re-quiping” her armour.
Shielded Meld: Does it even need an explanation, free boost on saves and AC
Maker’s Jump: with this you can enter to the dimensional dervish line, one level earlier before you can cast dimension door (which you should take in my opinion.)
Greater Shielded Meld: It just gets better.
Split Forms: Two Erzas…
Aspect & Greater Aspect: These abilities reduce your effectiveness while “armoured” but may improve your survivability without your armour.
Twin Eidolon: Your capstone. Unlike other summoners if you ever reach level 20 to get this, it will most likely work as “oh s~%+ button” since you can do the same ability with three different ways at earlier levels.
Summon Monster (SLA): Not much to say about this, common with every summoner yet not so useful for us since we want to be in “armour” all the time.
Spells and Cantrips: We have the best spell list for six level progression classes.
Depending on your build and attribute distribution, there are certain winners for each level.
Special Notice: Definitely take summon eidolon, rejuvenate eidolon line and the evolution surge line.
Race:
Personally and due to theme we will go with Human which has the whole package:
-Flexible Ability Bonus
-Bonus Feat (or the Focused Study for Eldritch Heritage line)
-Bonus Skill (or the Heart of Wilderness racial trait for extra survivability)
-Favored Class bonuses: +1 HP or Skill, or +1 HP or skill, for your Eidolon.
-Racial Feats:
Fast Learner (Int 13): a must have for this build giving you +2 HP per level while in your Fused Eidolon Form.
Improvisation: Look at me a skill monkey with only 13 intelligence (at least on low levels)
Improved Improvisation: Not that good IMO but it could have some meaning for a specific build.
-Personal Suggestion:
Definitely pick Fast Learner as it will improve tremendously your survivability.
The trick with Fused Eidolon at first level is that you add the Eidolon HP to your own as temporary HP.
F.E. Erza with 14 Constitution score and Fast Learner has 11 HP.
When she activates her Fused Eidolon (biped with Extra Natural Armor and Improved Ability Score Constitution evolutions) she gains a bonus 8 HP, plus +4 Natural AC bonus, improved Strength and Dexterity Scores, two claw attacks etc.
19 HP at first level is nothing to laugh at.
Ability Scores:
Since we are talking about an Epic Anime/Manga character and specifically for Erza, we will go with 25-point buy.
Str:13 (for power attack)
Dex: 10
Con:14
Int:14 (for skills and Combat Expertise)
Wis:12 (will saves and perception bonus)
Cha:18 (+2 human bonus included)
Eidolon:
Biped “Armor”
Medium Size
30ft Speed
+2 AC, Natural
Str:16
Dex:12
Con:13
HP:6 (without evolutions)
Evolutions & Progression up to 10th level:
1.Ability Increase “Constitution”(2pt), Improved Natural Armor (1pt), change claws to limbs feet (nice clawed boots)
2.Magic Attacks (for those rare low level opponents with DR/Magic.
3.(Reset evolutions) Ability Increase Strength & Constitution (2&2pt), Improved Natural Armor (1pt)
4.Magic Attacks, Improved Damage Claws
5.(Reset evolutions) Improved Natural Armor x2 (2pt), Ability Increase Strength & Constitution (2&2pt), Flight (2pt) (Hello Black Wing Armor)
6.(Reset evolutions) Improved Natural Armor x2 (2pt), Ability Increase Strength (2pt) Ability Increase Constitution x2 (4pt), Skilled (perception or acrobatics) (1pt)
7. (Reset evolutions) Improved Natural Armor x2 (2pt), Ability Increase Strength x2 (4pt) Ability Increase Constitution x2 (4pt)
8. Skilled or Magic Attacks or any 1pt evolution.
9. (Reset evolutions) Improved Natural Armor x2 (2pt), Ability Increase Strength x2 (4pt) Ability Increase Constitution x2 (4pt), Damage Reduction (3pt) or Weapon Training All Martial (3pt)
10. Improved Natural Armor x3 (3pt), Ability Increase Strength x2 (4pt) Ability Increase Constitution x2 (4pt), Damage Reduction (3pt)
Notes:
By Tenth level assuming that your normal ability score bonuses go to Charisma your stats while “Armoured”, without items should be
Str:24
Dex:16
Con:19 (17 +2 from ability increase of Eidolon)
Int:14
Wis:12
Cha:20
You also have Darkvision, Link, Share spells, Evasion, Devotion, Multiattack
BA:+8
HP: 10d8+30 plus 8d10+42 (82 temporary HP)
Saves without items: FS:+7, RS:+6, WS:+8
You use Evolution Surge spells for situational Evolutions like:
Flight (2pt/4pt) (Black Wing Armor / Flight Armor) , Immunity (2pt) at level 7+ (I’m looking at you “Flame Empress Armor”),Large (4pt) (Giant’s Armor),
Damage Reduction (3pt), Fast Healing (4pt)
You will probably spam Evolution Surge and Rejuvenate Eidolon like crazy so consider item creation feats eventually.
Also once available grab on Bracers of Armor 6+ until then cast Mage Armor.
For Feat progression I would go like this:
1st Fast Learner, Skill Focus (from Focused Study) or Toughness
3rd Eldritch Heritage (Draconic or Orc for optimization) or Power Attack
5th Combat Expertise
7th Cleave
9th Improved Eldritch Heritage or Great Cleave