One of Shinmyoumaru's spellcards is called "Shingeki no Kobito". The joke is that kobito literally means "little person" (which is what she is), while the "kyojin" in "Shingeki no Kyojin" literally means "big person", not to mention that the name of the spellcard is a reference to Shingeki no Kyojin anyway.
Do we even know that it's "Kobito" in this instance? Because it could've been a pun on "Kyojin", so he could've intended it to be "Shoujin" this one time. Or "Shounin", which is still close.