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Mha Symbolisms Don't Work Very Well Most Of The Time But This Is One Of These Cases Were HK Actually Did It Very Well - Blog Posts
Kinda ironic and poetic to think despite being one his favorite quirks, AFO probably has no idea about spearlike bones being his mother's quirk.
I mean realistically he doesn't have any way to know it, but I think he has an unconscious sentimental connection with his mom quirk as corny it sounds.
His favoritism even seem made him collect quirks that resemble spearlike bones in look and functionality, such as Rivet Stab and one unknown "drills" quirk. Both used at the same time during his last battle with All Might btw.
Also how we can forget the fact spearlike bones is also the last quirk he ever used? (On his original body at least)
Horikoshi definitely knew what he was doing here. I can't help but think it's brillaint despite the whole story is far from perfect.