Can I say that the Chrono Compendium as a whole could take on Crono? Think about it... We know where to get all the best weapons and armor, we know how to get all the cool tech's, and we know everything there is to know about him and all his friends - even before he knows it.
Okay, so that probably doesn't count.
Okay, when you put it that way it actually sounds a little creepy... and it's certainly saying a serial killer or rapist could take him down like say Franz or Pierre? GASP! Yakra and his chancellor kidnapping ways put to work on Crono!
I think Ike (from Fire Emblem's Radiance Chronicles and SSBB) would be able to take Crono. Ragnell VS. Rainbow. Ragnell wins due to sheer mass and weight. Rainbow snaps like a twig.
GREAT... AETHER!!!
SD: Would be bigger, but don't want it too big or it's spam.
Good attempt but if that were necessarily true, then wouldn't Cloud be able to do it since Cloud is kinda tougher and has an even heavier sword he carries even more easily? Not to mention we don't know the weight of the Rainbow and the weight issue... wouldn't that make it harder for Ike?
Even if he can carry it pretty easily, he still has a slower swing and as proven well in an episode of DBZ I remember where trunks battled Cell,(that's my example since DBZ and Chrono had the same artists it's done many other places as well)power is squat if you can't even keep up with the opponent and Ike is a slower character thanks to that weight so really Crono with his Confuse attack could easily spin around him so fast he'd have no chance of seeing him AND Crono could be slashing rapidly at the same time(he just doesn't feel like showing off or something so he slashes four times in the game).
Lastly even so, Ike got the crap kicked outta him by characters that Crono could whup the living daylights out of. He may have weight, but we don't know just how heavy the rainbow is since they don't make a bother of that but I'd imagine with the strength behind it, with power comes weight so it's gotta be pretty heavy as well(Crono IS extremely muscular and that's probably why he swings so fast, moves so fast, and treats everything like it's light and slow cause he's too damn fast)and even if it were heavier, the material of the Rainbow wouldn't snap so incredibly easy, and Crono's speed puts him too far ahead for Ike to even touch him anyways.
And of course there is always the cheap method we bring up with practically EVERY character pitted against crono... Luminaire, yada yada, all powerful, blah blah, you've probably picked up the routine since we've done it a thousand times before.