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.
YMMV: Ar tonelico
Game Breaker: Not really needed considering you have the Reyvateils doing the damage more than your vanguards, but you can actually make anyone (though Lyner gets to use his Wind Slash even before going through the first level of the battle phase) into a Glass Cannon capable of dealing up to 25,000 points of damage. Of course, said party member dies after one hit. The real game breaker though is when you revive them, the person revived gets to act immediately on their turn. Long story short, Wind Slash everything into oblivion. Of course, you do get called out by your current Reyvateil whenever you rest at a camp.
Ho Yay: Ayatane's relationship with Lyner is a little too close for mere friends. Carries over into Cross Edge.
Moe: Saki certainly looks this way. Not to mention the series in general draws upon a wide variety of things considered "moe" in some form or another - and even parodies them with the attack item Moe Firepowder in Metafalica.