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swpkmn: A hint for a hint ? the 'portal' part is about the door in the upper portion of the portal hub map; but I've got a question of my own: what skills/equipment did you use for boss fights ? I'm getting slaughtered even by Anastasia, who (HP-wise) is the weakest of the three.
The door is gone, but nothing happens in the area behind where it was. What exactly is supposed to happen there? I am not exactly sure how to help you with your issue, but I will do what I can.
The Hero's skill-set mostly consists of what could be considered buffs. Some of those skills can do things such as temporarily give one character 10x Max HP and luck for 3 turns (召還一時的な依り代), giving one character 50% MP regeneration for 5 turns (闇の怨念の憑依), giving the party 25% HP regen for 5 turns (蠢く生命の流し込み), dealing damage to 4 random targets (闇の抱擁), and dealing powerful damage to a single target but healing the target's MP (一体化する触手).
Chris's first skill (魔の奔流) heals every (conscious) party member's MP to full. This is useful as all of her skills require MP. She also learns a skill that raises a character's Magic Attack/Magic Defense stats by 10x (神聖で尊い液体), which is most useful when cast on herself. The skills "偉大なる雷光" and "紅い火の海" do powerful single-target damage but also heal that target's MP, while "雷光の雨" and "爆裂する紅い火" do less damage to 4 random targets (Like what the Hero has, but different elements). I find the random target spells more useful when there are many targets, and the single target more useful when there is just one.
The skills "クンカクンカ" and "オーガニズム" heal your character's TP by 30/50, so they are most useful on Jeanne, who mostly has TP skills. Her first transformation allows her to basic attack multiple times in one turn while it is active, while the second makes her reflect or counter every enemy attack that targets her while it is active (they cannot both be active simultaneously). She can learn a passive technique to automatically revive in battle the turn after being KO'ed, and she also learns a "powerful single-target attack that also heals that target's MP" (紅い火の海), but doesn't naturally gain the MP necessary to use it.
Charlotte is mostly the cleric, but also has some other uses. I have only found one transformation for her (Am I missing something? The other heroines have 2 each). The skill "穢れの浄化" heals some HP as well as ailments caused by enemies (ailments meaning statuses with purely negative effects, like poison, doll, and estrus). "生命の救済" revives an ally, "邪悪の抱擁" is the "powerful single-target attack that also heals that target's MP", and "制裁" does less damage, but can instantly KO some enemies.
I have trouble reading what most items do, so I try not to equip items with complicated descriptions that may cause something I don't understand. It seems like the equipment and the status effects have both strengths and weaknesses that are not clearly defined. I do try to make sure I focus on Chris's Magic Attack and Jeanne's Physical Attack, since they never seem to learn anything for the other offensive stat. The transformation skills learned by the heroines are also very useful in long battles, but they only last a few turns, and it can be hard to keep track of when they will wear off.
What difficulty do you mean, though? I have not been able to beat any of the final bosses at any difficulty above Normal, even at Level 99. I have noticed that the following items raise character stats. It might help to use these. The first group of items can be be dropped by enemies and found throughout the game. I am not sure where the second group is obtained. (I would guess from events?):
肉体の物語: Raises a character's Max HP by 50.
精神の物語: Raises a character's Max MP by 30.
攻撃の物語: Raises a character's Attack by 5.
防御の物語: Raises a character's Defense by 5.
魔力の物語: Raises a character's Magic Attack by 5.
魔防の物語: Raises a character's Magic Defense by 5.
速さと運命の物語: Raises a character's Agility/Luck by 5.
☆刹那を刻む砂時計: Raises a character's Agility by 500
☆金剛の肉体: Raises a character's Defense by 500
☆暴走する破壊衝動: Raises a character's Attack by 500
☆受け継がれし叡智: Raises a character's Magic Attack by 500
☆魔法の障壁: Raises a character's Magic Defense by 500
☆福音: Raises a character's Luck by 500
☆湧き上がる生命力: Raises a character's Max HP by 1000
☆大いなる魔力の器: Raises a character's Max MP by 1000