User blog comment:KnocknickKnock/Celestial combination attacks with Lucy"s 10 zodiac keys./@comment-3424593-20140310043620/@comment-24066070-20140310144121

The One Magic may not be a magic as those shown in the series so far (e.g. fire/water/heavenly body/requip/etc), but rather be some sort of ability. The One Magic was stated to be at the root of all modern magic, so it likely refers to the ability to use magic or something which transcends magic (e.g. curses used by Tartarus)

I think "obtaining the One Magic" refers to someone being able to understand the very essence of magic and thereby being able to learn all or at least many different kinds of magic. Something like the Sage of Six Paths from Naruto who invented all ninjutsu after he inherited the power his mother got from eating that forbidden fruit.

Therefore I don't think the One Magic is something that can be sealed inside someone, but rather something which is mastered over time.

About Unison Raid, Jellal said that a monk (singular) searched for it during his entire life. But, since it requires at least 2 mages, it makes sense that 1 guy couldn't pull it off. Many chars have already used it in the series, so I don't get why ppl treat it as something exceptional or hard to learn. Just have 2 mages pool their magic and you get Unison Raid.

About Lucy summoning all her Spirits in front of the Spirit King when she saved Loke, this was never clear to me. Did she summon them, by her own power, or did they just show up as a statement to the Spirit King, since they shared Lucy's opinion and didn't want their "leader" Loke to die? If they did the latter, then it isn't an indication of Lucy's power or potential.

Concerning her growth rate, I don't find it that spectacular tbh. She can summon 2 Spirits due to Second Origin, she got that whip for meelee combat from Virgo and she practised Urano Metria after learning the incantation from Hibiki and her mastery over the spell isn't that great yet. So all her power-ups have simply been due to plot reasons (Second Origin), befriending her Spirits (the whip) and simply gaining more Keys. On her being a mage for only a year, I'm not sure. She is only an official mage belonging to an official Guild for 1 year, but she was already a mage before joining FT.

If you consider her skilled because she surpassed ppl like Vijeeter, then there are many skilled mages, since Vijeeter and his fellow losers who only act as furniture aren't that talented.

I would even say her growth rate is the slowest of all the Team Natsu members, since the others got way more power due to various reasons.