Eiyuden Chronicle: Hundred Heroes

Getting Nowa to 99 is not hard at all, when you unlock the proving grounds mystery door.

Once you have it unlocked the battles there will easily take you from the 50's to 90's in a few battles doing the endless mode battles. (endless mode is unlocked after you completed the normal mode)

The last few levels will take longer but be sure to have both the Accent badge and growth badge to speed this up.

*This should be saved for last as i used this right away and was so overpowered the rest of the game was a cake walk kind of ruining the rest of the game for me.

As you probably already know by this point, in Eiyuden, underleveled characters get huge amounts of EXP (and each level only has 1000EXP, so with all the EXP badges and supports, some people can and have jumped from levels 30-50 to level 99 in a SINGLE battle in Endless Mode on the Ancient Seed floor, if supported by a stronger character that can one-shot the enemy party). If you intentionally keep Nowa underleveled throughout the adventure, here is a video example of how ridiculous it can look to abuse the game's leveling mechanics:

https://www.reddit.com/r/EiyudenChronicle/comments/1cgpt5a/h...

However, if you have already leveled Nowa up beyond around level 80, it becomes impossible to take advantage of this powerleveling strategy. You have to grind things out the slow way. This is especially so now since in May there was a patch that eliminated an item duplication glitch, which would have allowed you to duplicate the endgame EXP badge (the Ascent Badge, found in the final dungeon, Gardhaven Castle, in a chest. There is only one in the game unless you replay it on NG+).

That was the situation I found myself in. Especially at level 97, under normal circumstances with your full, traditional party, every Endless Mode boss battle might net Nowa only 30-40 EXP. So, keep these in mind:

1) Always keep Yulin as support in order to boost EXP gains.

2a) EXP is divided between all your conscious party members. This means that if you want to do this quickly, you need to duo/solo boss battles in the Endless Mode trials, which are the only late-game situation where you get meaningful EXP at all at these levels.

2b) There are plenty of combinations that probably could work, so long as you have Nowa and a huge damage-dealing AOE character. The best options seem to be Leene and Momo. If you choose Momo (for instance, if you missed the Aleior window and you don't have Leene), you MUST equip the following:
i) Rune of the Mage's Path (greatly sacrifices magic defence for magic attack)
ii) Rune of the Mage's Pinnacle (greatly boosts magic attack if the mage is placed in rear)
iii) Rune of Conflagration (highest-level fire magic damage)
All other available runes should be magic attack-boosting (Arcane Magic, if possible)

If you choose Leene, you MUST equip the following:
i) Rune of the Warrior's Path (greatly sacrifices physical defence for physical attack)
ii) Rune of the Warrior's Pinnacle (greatly boosts physical attack if warrior is placed in front)
All other available runes should be physical attack-boosting (Tremendous Power, if possible).

In either case, include a Rune of Water on Nowa so you can use Recovery Wave, as on Endless Mode's first floor (which we will be repeatedly restarting) you will not have access to items like you did in the normal mode.

Nowa should be hardy enough to survive at least two rounds of solo attacks from the boss(es) before needing to heal. He should ideally also have the Rune of the Warrior's Pinnacle and should be placed in the front row. Equip primordial armour on Nowa, which you would have won while completing the normal Hero's Trial. The other person can have League armour (purchaseable in the postgame from the armour shop in the Trading Hall 2F).

Of course you should also fully upgrade all their weapons at the smithy, if you hadn't yet done that at this point.

3) Equip the Ascent Badge on Nowa.

4) Keep rerolling the Endless Mode's dungeon until you get Kogen, Astraea the Judge, or the Goblomancer. These three boss battles have multiple enemies and give you credit for each additional enemy you kill, as the game seems to scale down the EXP gained from each enemy (rather than the total EXP gained at the end of battle). This means that it is in your interest to fight multiple enemies wherever possible. I assume that the Dead Countess fight might also give you this benefit (she summons her three minions) but I did not fight her personally during my final EXP grind.

5) Once you get started, start with an AOE attack from Leene (or Momo) to clear the first two floors. Start with the AOE attack on the boss battle also (followed by Nowa's MP-consuming AOE). Eventually, the boss will target Leene/Momo. If they survive the first turn of attacks, do not heal them; you want them to fall unconscious before the battle ends, but you also want them to soften up the enemy as much as is possible.

6) Use Nowa to finish up anything Leene (or Momo) were unable to finish. The full round of EXP should go to Nowa. When accompanied by all the other boosts, I got around 300EXP for wiping Kogen's party at level 98, for reference.

7) At the end of each floor, you will be prompted to add 3 members to your party to continue. Just quit out and talk to Selbineth again and roll for the same bosses I mentioned in (4) rather than continuing deeper into the trial.