Hard Quest Farm Guide

In The Alchemist Code, as you progress through the story, you will unlock ‘hard mode’ versions of different quests that will give you access to farm character upgrade shards. You'll want to start farming shards for the more useful 4 and 5 star characters as soon as you have access to these missions, even if you don't have the characters yet, because then when you get them you’re able to limit break or enlightenment that characters right away, which are essential for nearly every unit in the game.

The following 4/5 star characters are ones you want to consider farming, and are roughly ordered in how quickly they become useful to new players. Note that there are now many good farmable units so you may have to prioritize which to farm first; units which you should prioritize will depend on what units you already have. Additionally, 1-3 star units are all farmable but for the most part there are better ways to obtain them. 3 star units are commonly gained from summons, and you're likely to get all the good ones (Vanekis, Alyu,etc) purely from the free summons you get as a new player. There aren't many 1-2 stars that are worth farming right now, but you can collect many of them with zeni from Anna's Shop, if you want to use them.

Between the AP from the Daily Milestone Quests and AP regen you are able to farm 20+ units a day and still save some AP for other content. You need to be efficient about who you farm because there are a lot of good units to choose from. The content is more geared mono element team with enlightened units or at least level 75 units. Even farming 3 times/day/unit plus bonus from x2 Hard Quest (we usually get this for a week per month), you are looking at around 105 shards a month not counting duplicates, so it takes about a month and a half to get a unit to level 75 and about 5 months of farming to get units to a good enlightenment level.

Early Game
For new players, you should reroll for a carry unit (you can look at Reroll Guide), using some farming slots and try to complete a team around that unit as soon as possible. By doing this, you can have a good mono element team that can help you clear the old content and possible for higher content. For other elements you can fill in good units with low investment that are viable at lvl 75 or lvl 80. Before farming a unit long term you should check if they have a job+ that is only available occasionally on the Job Upgrades list. Many job+ are seasonal and only return yearly, some may only return a few times a year. The units listed below are all at least reasonably functional without their job+, depending on whether you have acquired their seasonal job+ there may be other high priority units worth farming.

Example of some of the better units to farm for a newer player:
 * Fire:
 * Emma viable at LB15 with her job+; Diviner is a good job. Her job+ is available in the A Bond More Enduring Than Starlight event in the Event Archives.
 * Chihaya viable at LB15; job+ can be farmed in the Wadatsumi's Dance event in Multiplay, she can use Leaden Feet which can reduce agility of all enemies on the map and debuff their slash resist, and can also quicken.
 * Lupinus viable at LB15; mostly used as Chronomancer (but sometimes with her other jobs) for the Arcana Ratty reactive from Agartha Summoner in raids. Typically you will leave her main chronomancer untrained so she will quicken on auto.
 * Water:
 * Ankh viable at LB0; ideal at LB15, has good base stats and hits hard once you get Overdrive unlocked from his 3rd job.
 * Shayna viable at LB0; ideal at LB20, with Holy Brawler [Shura] charge up, she can hit very hard with Supreme Battle Trance.
 * Elizabeth viable at LB0; ideal at LB15, used primarily to prevent status effects with her Professor job and provides quickens with her Chronomancer sub.
 * Lofia viable at LB15; ideal at LB20, her job+ can be farmed in Sweet Aspirations in the Event Archives, used primarily as a Chronomancer and for charge time down and delay on raid bosses.
 * Thunder:
 * Gerald viable at LB0, ideal at LB15 with his job+, has good base stats and access to a charge up, can also be run as Dragon Cavalier [Rudra] as needed. Becomes extremely strong with his archived job+ from Steel in Hand, We Defend.
 * Zofia viable at LB15, hits hard, has access to Thunder Res Down which can be helpful in Raids.
 * Mei Fang viable at LB15, hits pretty hard and has good bulk as well as the ability to inflict some status effects.
 * Wind:
 * Ramses viable at LB15; ideal at LB20, he does strong damage, has some area of effect abilities and with access to Dragon Cavalier [Rudra] he can teleport.
 * Setsuna viable at LB0; ideal at LB15 with her job+, all three of her jobs are relatively viable depending on what you want to use her for. She is especially strong with her time limited job+ from A Lone Swordswoman and Her Siblings. With her Holy Brawler [Shura] charge up, she can do fairly strong hits.
 * Balt viable at LB15; very fast, with consistent high damage and strong evade. His J+ can be found in The Desert Merchant in the archives, where an additional shard farm on top of his Babel Chronicle farm is also available. This means he can be farmed 6 shards a day, double the amount of most character shards.
 * Natalie viable at LB0; ideal at LB15 with her job+, is used primarily as a Professor to prevent status effects but can also be used as a Battle Mage for wind magic attacks. Her archived J+ is from Steel in Hand, We Defend.
 * Light:
 * Chloe viable at LB15; ideal at LB20, job+ can be farmed in Reclaiming the Scarlet, she is a tanky unit with decent damage and some healing skills.
 * Zain viable at LB15; job+ can be farmed in Reaching the Gates of Sin by Dawn in the Event Archives. You can obtain him for free from challenge board 7. He is primarily a damage unit (including AOE), with some additional utility.
 * Neica viable at LB20; ideal with her job+. she has very high MATK, although she is a little bit slow but the amount of damage she can bring and her upgrade reactive (defend) can make up for that. Her limited time job+ is from Magically Dyed Colorful Egg which is an Easter themed event.
 * Spica viable at LB15; her job+ to War Princess of the Shining Star can be found in Pitch-Black Blood Relations - The Unfulfilled Promise in archives
 * Dark:
 * Zahar viable at LB15; but does not shine until 2nd enlightenment gate is unlocked (unlike most units, the bulk of his power is not acquired until he has this so he is more of a long term investment). His sword can be farmed in Babel Chronicles, he can put down really high damage without charge up and has good jewel regen and self sustain capabilities. He is a high priority to farm even if you do not yet own him, since he will be very powerful long term and needs a lot of farming to get to a good level.
 * Kudanstein viable at LB15 but ideally wants enlightenment for reasonable stats. He is a strong damage unit with teleport cross attacks and a strong charge up ability. His gear can be farmed in Sacred Stone Memories - Demonic Spearman and his job+ can be found in Sacred Stone Memories - The World's Laws Begin to Fluctuate.
 * Basheeny viable at LB15 but ideally wants enlightenment for reasonable stats. He is a decent damage unit with high speed and mobility and a strong charge up ability. His gear can be farmed in Sacred Stone Memories - The World's Laws Begin to Fluctuate.
 * Jin viable at LB15; his job+ can be farmed in Return to the Underworld in the Event Archives. He is primarily run as his job+ but can also be run as Warrior [Gigantes]. He can be used for damage, resistance debuffs, status prevention, or with his berserker mode in multiplayer.
 * Priscilla viable at LB15; she is good at AOE attacks and has some self sustain ability.
 * Albea viable at LB15; she is good at long range damage, but not as high damage as other units, and also has some useful debuff skills.

Mid Game
In the mid game, increase the number of units you are farming to improve your teams and provide niches. At this point, consider pre-farming units with a time limited job+ in anticipation of an event rerun. It would also be beneficial to vaguely understand the JP meta to begin farming for future job upgrades and other updates. Also consider farming some Babel Chronicles units such as Letitia, Gerald, and Cheryl to your farm list even if you don't own them and other valuable limited units such as Judith. This way you can transmute them if you never pull them, or save shards to raise them immediately after pulling.

Late Game
In late game, when you have good teams in every element, you can just work on favorite units or fill in any weak spots to give yourself more flexibility.

Unit Limited Farms
Note that there are some unit limited farms. For these you must own the unit to farm and they are limited to 1 clear a day. If you own these units it is generally a good idea to farm them as it can take a long time to get enough shards. You must clear most of the story in order to unlock them. Neun, Vier, and Sieba in particular are high value targets to farm if you own them, but usually it is worth farming any unit limited quests you have access to.

For More Information

 * See Shard Farm Priority for a suggestion on which character shards to be prioritized.
 * See Farmable Character Shards for a list of which hard mode quests provide which character shards.
 * See The Alchemist Code Global Tier List And Build Guide for information about the current state of units or get some idea about the potential future state of units from Tsubaki’s JP Tier List (note that Japan gets upgrades in very different order and global has some units that Japan doesn't have, so don't take these future ratings too seriously)
 * For advice more customized to your account, feel free to ask in the Discord channel in #ac_questions.