These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Mad Dog in Sundown's chapter, though this may be intentional. Defeating him on the second fight removes an additional scene from that chapter's ending.
O-DI-O from Pogo's chapter is really simple if Bel learned her singing attack.
OD-10 in Cube's chapter can be easily defeated by standing next to him and using High-Speed-Op and Upgrade, Cube will counter each time he is attacked, and become stronger with each heal. Eventually, he can do more damage than the boss has HP.
Depending on how you play through the chapter Oboro's Final Boss can easily be killed or be ungodly hard.
The final battle against Straybow in Oersted's chapter. While he has improved some since the fight at the beginning of the chapter, he's still relatively weak in comparison to the bosses fought before him.
Level up Sundown enough in the final chapter, and he learns an ability that can usually do 999 damage in one hit, making almost every fight an Anti-Climax Boss.
Alternative Character Interpretation - Alicia can be seen as either two ways. A) Always in love with Straybow and Oersted was just reading too much into context. Or B) Shallow typical ditzy princess who only crushed on Oersted after kicking ass in the tournament and was easily seduced and manipulated by Straybow, whom simply wanted to ruin Oersted out of hate either way. Depends entirely on how much you read into things really.
She can also be viewed in more of a sympathetic light, in that she truly did have feelings for Oersted but was emotionally manipulated into falling in love with Straybow. If you buy into the idea that Straybow was the one behind her kidnapping in the first place, this seems like a perfectly viable interpretation.
Breather Level: Cube's chapter only has one required boss battle, and it doesn't have a single Guide Dangit. That doesn't mean it's boring or that you can't die in it...
Sundown's chapter has a total of five battles, of which one is optional (and eliminates one of the others if you choose to fight), three are laughably easy, and one is against the chapter's boss and can be made significantly easier depending on how you set the traps.
Cliché Storm: One way in which the game suffers is its short chapters - the plots are general and predictable, and you tend to know exactly what you're getting from them. Whether that's a bad thing is up to your interpretation, but it gets subverted near the end of the game either way.
Complete Monster: A number of Odio's human reincarnations have signs of this, but in particular:
Ode Iou, as his goal was to prolong fighting in Japan just so more lives are spent. Ends up transforming into a giant frog/snake monster.
Odie Oldbright, who thinks 'cruel and brutal murder' is the path to becoming the strongest. He even brags about the act, as if he accomplished some great feat.
Oboro's chapter can be played this way, killing every single person you find, even innocent women. Granted, some of those 'innocent women' turn out to be demons.
Game Breaker: The Cola Bottle from Pogo's chapter can become this in the final chapter. Just make sure to equip it to Pogo as an accessory before his chapter ends, and it'll carry over to the final chapter when he joins your party. The Cola Bottle is an infinite-use item with an attack that can deal 999 damage to almost every minor enemy in the game (and even some bosses!). Needless to say, the final chapter becomes a breeze with this in your arsenal.
In Pogo's chapter, there's "Laa Laa", an attack Bel learns at Level 7. Take an hour or so to build her up before examining Zaki's firepit, and you can one-shot O-DI-O. As in the chapter boss.
Goddamned Boss — Voice Heart. After encountering him several times in an extra dungeon, you will want to scream "JUST LEAVE ME ALONE." It's quite gratifying when you get to tell him off and kill him at the end of the dungeon.
Cube's chapter, once the Behemoth gets loose and things start to go to hell. The tense music doesn't help.
Oboro's chapter: that weird person(?) who runs away from Oboro emitting some kind of horrible roar.
One attack used by the final boss is also accompanied by a horrible wail. The visuals make it far creepier, too.
That would be "Saint Alicia". The aforementioned visuals are that of an angelic-looking female figure hovering over the target, and then quickly melting into a horrifying hag with a mouth of fangs. The worst part of it is the name. Saint Alicia. Oersted is so consumed by hatred that that is how he sees his once beloved Alicia.
In the Final chapter, the kingdom that the Medieval chapter took place in is eerily quiet. What happened is hinted in a number of places, and then all but outright said in Akira's secret dungeon: Everyone's dead. They either died during the events of Oersted's chapter, or were killed by Oersted as Odio. Even the little kid who still believed in Oersted.
The prelude to the Death Prophet in the final chapter. You're just minding your business, probably running away from battles when things go south. And suddenly, after retreating, the music stops and an ominous message like the Grim Reaper warns you that death awaits those who run away too much, and starts counting down to zero every time you run away. When the countdown reaches ZERO... it comes to you. A black panther monster that can easily turn you into stone. Unless you're the type of keeping count of how many times you run away, the Death Prophet's warning comes off as chilling and shocking.
Player Punch: Amongst many, die while piloting Buriki Daioh. Akira and Matsu revive as spirits and Matsu says "You Bastard!" to Akira before the player returns to the load screen, feeling a lot like the You Bastard in question.
The Kung Fu chapter. The Master takes in three bright, promising pupils who all show signs of being inheritors of Shin San Ken, and then two of them are murdered by Odi Wan Lee's goons. Even worse is that, once you know how the game chooses which ones live, it's basically you deciding which ones die. Go ahead, try not to feel bad when you replay the chapter, with that knowledge.
O-D-O has Bite, which can do massive damage to anyone in the party.
Ode Iou has Poison Serpent Whip; while it doesn't do much damage, it covers almost the entire battlefield in poison spaces. Also, Drink Blood is pretty strong and heals Ode Iou.
Odi Wan Lee has Kuang Zhuan Yan Wu, which can easily kill the inheritor when you face him.
O. Dio has Gatling Shots, which almost always does enough damage to result in a One-Hit Kill.
Odie Oldbright has Acro DDO, which can kill Masaru in one hit.
Two hits, if the player's lucky.
The Inka Kuruu Odeo has Liquefied Human Curse, which does random damage, but normally does plenty.
OD-10 has Driveback and Driveback-Counter, which deal tons of damage and create electric panels; however, he will only start using them if you cast Info Research on the middle of his sprite to change his graphic.
The Demon King's strongest attack instantly stones anyone hit by it. This can, however, be cured with Uranus's healing move. God help you if he gets stoned.
Pure Odio has Cancel Ray, which instantly disrupts any attacks you have planned, but he and Illusion Odio also have Life Eraser, which will stone you for sure if you don't have the Ariel Equipment. Pure Odio likes to use Life Eraser (which also heals him for any damage done) after every move you make, which means hurting him is nearly impossible.
If you play as Oersted during the Final Chapter and have to face the heroes as the Final Bosses, you'll find that these attacks still work wonders, but they have limited range, which is why they aren't used often in battle.
Optional boss Amakusa in Oboro's path has Electric Barrier, which deals 120+ damage and surrounds you with electric tiles. Oboro has about 160 HP if you've killed everyone in his path up to this point. And Amakusa likes to use this attack twice in a row. (This is not a Bonus Boss, but rather one you must fight if you take a specific path through the chapter.)
That OneBonus Boss: King Mammoth. (and Lord Iwama., mostly if you attempted a pacifist Oboro run.)
When it comes to required bosses, Max Morgan from Masaru's chapter is an utter bastard. If you slip up just once, he'll kill you in three hits. (And remember, Masaru has to take hits in order to learn his skills!)
Gynophobia, the second-to-last boss in Oersted's chapter. Giving a boss two attacks doesn't make her fair when one of them heals her for all the damage she deals and the other puts you to sleep. And the one that puts you to sleep has a massive range. Even better? You fight this boss alone.
The Woobie: Cube. And depending on your temperment, Yuan from the Kung Fu chapter.