Eiyuden Chronicle: Hundred Heroes

This is not for completing "The Proving Grounds" dungeon through the main story of the game but for completing "The Hero's Trial". The trial becomes available after building the "Mysterious Room" in your castle and features a series of battles with all the major enemies in the game (plus a few more). There are 26 floors (aka levels) and every level but the last consist of two minor enemy battles then a boss battle. After every five floors or five bosses your HP and MP gets replenished and you are allowed to quit and resume from there. While the trial just like the main game is not that hard I would advise to try this at the endgame, when you upgraded everything and collected all the characters. The Trial was deliberately built in a way that almost any number of team combinations are viable but I will provide the simplest team and tactics that allows anyone to complete it with the minimal amount management. As I said this should be an endgame activity or it will become unnecessary longer and harder so I expect you to collected things you can't skip and upgraded your castle as well. If you can't find something I refer to do not worry, this team composition is extremely lenient, it doesn't use anything but basic attacks, some SP attacks and items you will get plenty of. If you actually start using magic or other items it will become even stronger. You should be able to start this with ease after finishing the story (above lvl50). I won't mention armor or weapon levels as I do expect you have the best.

The Team
Front: Nowa, Dijkstra, Reyna.
Rear: Isha, Momo, Leene.
Support: Perrielle but it doesn't matter as you will see below.
The idea behind this team is to build an almost impenetrable front row you rarely need to care about while dishing out tons of damage. If someone gets really hurt then the fast team members can heal them reliably. Most enemies attack the front row, the only real danger is a few AOE attacks that can hit everyone but the front row will survive and recover everyone else (this will almost never happen, your team is very sturdy aside from Leene).

Nowa
Runes: SP (+1SP at the start of the battle), SP Charge (+1 SP per turn), Mighty Power (+10% strength), Warrior's Pinnacle (Fiery Spirit if placed in front)
Accessory: Eggfoot Stone (+25 strength, +25 magic) but anything with a strength buff is good.
One of the strongest fighter among the heroes is here to deal damage in every turn (also he needs to be lvl99 for another achievement). His job is to simply Swinging Slash (2SP) over and over. He is the squishiest member in the front row so he may require some healing from time to time.

Dijkstra
Runes: 2x HP or Defense, SP Conversion Defense, Knight's Path (half damage and magic for twice as much defense).
Accessory: Super Lucky Badge for those sweet rare rune drops and healing items.
Dijkstra is here for one thing: he will Powerful Warcry in every single turn. The Warcry boosts the damage of everyone else tremendously and ALWAYS first in a round. His other job is to tank damage in the front row. He will only take minuscule damage from almost every source, seriously like ten or less.

Reyna
Runes: 2x Mighty Power (+10% dmg), Water (never used it but a failsafe if item usage is forbidden and the casters are occupied).
Accessory: Ruby Bangle (+30 dmg), she really needs this as her output is pretty low against most enemies.
Reyna is in the stereotypical tank role, she will rarely if every get more than a few damage. She does a decent slash with her sword in the meantime while protecting the back. She gets a small utility by the end of the Trial: she is guaranteed last in every turn so she can begin healing with an item after everyone got damaged. She is also good to patch up someone who can wait.

Isha
Runes: High Magic (+10% magic), Arcane Magic (+15% magic), Mage's Pinnacle (Awakening if placed in the back row). She has two 4 dot magic slots you can put anything in if you want to use magic. I had Pure Water and Brilliance on her as she was always my mega healer / booster but never used them here.
Accessory: Tanzanite Bangle (+30 magic).
Isha is one of the best casters and amazingly fast compared to the other characters until lvl80. She is guaranteed to start first (after Warcry) against everyone but Fenrir (floor 20). This gives her insane utility with healing as you can be sure everyone is in top shape before the first blow lands in every round. You don't need to use her magic, she is fine with the 300 healing, 150 healing (everyone) and revive with 200HP items. I never used her magic in the trial and while sometimes others had to help I was fine. If you find some 500HP (everyone) items keep them for the end where some bosses can hit really hard with AOE attacks.

Momo
Runes: 2x High Magic (+10% magic), Mage's Path (half defense, double magic), Mage's Pinnacle (Awakening if placed in the back row). One 4 dot and one 3 dot magic slot to put anything in. I went with Conflagration and Currents but never used them.
Accessory: Masquerade Mask (+100HP +50MP) while she is nowhere near as bad as Leene she needs a bit of HP to survive.
Momo hits like a truck but with a staff. The basic attack is already insane and will only get better as the magic stat is insane. The health and defense is decent, even with the drawback.

Leene
Runes: Warrior's Patch (half defense, double strength), SP+ (start with +2SP), SP Charge (+1SP in every turn), Tremendous Power (+15% strength), rest is SP Conversion: Mighty Power (+4% strength for every unspent SP).
Accessory: Malachite Bangle (+200HP)
Lenee is the most flexible character in the entire game with 7 slots you can put anything in. There are a bunch of options for her but I went with one where she can wipe the normal enemy waves right away and do strong damage against the boss as well. The only drawback is she became really squishy as her base defense is already low. She will die regularly if targeted, even with the +200HP but it is worth it. Her Full Force Clacker comes first after Warcry and wipes out every normal enemy right away. So in the inbetween rounds you just cast it and go on. For bosses use her normal attack as the SP conversion makes it very strong (and you are always topped). If the boss has servants then just Clacker them away.

Perrielle
She is a decent support for the battles but we won't rely on support because we will use them to nullify a drawback in the Trials. Namely you need to replace one member of the team after every boss. This would make things much more complicated because you would need to create many good characters to complete the Trial with (the pool is also random so you can't rely on a few extras). The only way to avoid this is to always switch out the support. That way you can bring your best characters all the way to the end.

General tactics
As I said above for the waves with normal enemies you can just Warcry and Clacker them away. Both Dijkstra and Leene are guaranteed to act first. For the boss waves it is mostly just attacking with everyone but Dijkstra and drop a healing/revive here and there with Isha when needed. The bosses will die incredibly fast, you don't really need to use the gimmicks either. As the team gets close to the end both Momo and Leene becomes faster than Isha (who is already faster than almost anyone) so you can play around with the healing order. With that said Momo and Leene should always attack if possible as they do a lot of damage. Nobody ever used magic in my team so if you feel thing are hairy feel free to drop a massive heal and damage boost with the casters. The Super Lucky Badge will guarantee you will swim in healing items and you can bring 20+ of everything you may need to make it safe.

If your bag is overflowing don't forget to pick up the runes and shards you will find as many of them are unique to this mode and you are required to collect them for other achievements!