天ノ弱 (romanized as amanojaku) is a Vocaloid song by composer 164, featuring the voice bank GUMI (Megpoid). The title is a deliberate homophone: 天ノ弱 reads literally as "heaven's weakness" but sounds identical to 天邪鬼 (amanojaku), a trickster creature from Japanese folklore known for doing the opposite of what it is told. The lyrics play on this same contrary spirit, tracing the self-deceptive inner monologue of someone who insists they have moved on from a past relationship while their words betray lingering attachment. Originally released on 164's 2012 album THEORY -164 feat.GUMI- with a music video by 鳥越タクミ, the song became a fixture of the niconico Vocaloid scene and was picked up across multiple SEGA rhythm-game franchises. It landed in maimai GreeN on January 23, 2014, making it one of the earlier Vocaloid tracks in the series. Over time its in-game genre label shifted: it debuted under VARIETY, was reclassified as niconico in GreeN PLUS, and from PiNK onward has been listed as niconico & VOCALOID. In maimai, 天ノ弱 spans two chart generations. The original Standard charts from the GreeN era include a level-13 (13.3) Master chart co-designed by mai-Star and はっぴー, who originally credited their collaboration under the joint pseudonym "合作だよ." When maimai DX Splash arrived in 2021, the song received a full set of DX charts integrating Touch notes, headlined by a Master layout (12.8) by designer シチミヘルツ and an Expert chart by 小鳥遊さん. The song has also appeared as a launch title in both CHUNITHM and オンゲキ, further cementing its status as a cross-title Vocaloid standard.