Larcade has never known what it is to be loved by someone… so not even by Zeref? His own father?
Zeref might be doing things wrong but from what we’ve seen we know that he wouldn’t neglect his own child. (e.g trying everything to bring his brother back from the dead, ending up cursed and immortal as punishment.) which makes me think that Mavis didn’t actually give birth to Larcade BUT both Mavis and Zeref’s DNA are within him.
Unless Larcade is in fact their son and Zeref neglected him of love to build him into an insensitive machine/weapon for his own advantage. Or through no fault of his own due to Ankhersam.
Larcade has never known what it is to be loved by someone therefore ending up incapable and closed off to emotion, “a state of mind devoid of anything” but the only one who can defeat him is his mother, Mavis.
Mavis never knew what it was to be loved by someone growing up (until she met Zeref and FT) but she never wavered, she grew kinder and valued more.
Mavis will defeat Larcade with love. A mothers love.
