Of course, Nei and Souta are as adorable as always, but I think there's something else funny hidden among the lines here as well...? Why did Nei's dad bought a potion like that...? And, in hindsight of what happened 2 chapters ago... maybe he thought to do something before his marriage would get ruined because of his wife's Ara-ara tendencies...? XD lol
And on a side note, potions like this allow an alternative solution to question about whether Nei likes Souta because he's a shota and if that would be how it is (I don't think it's that though), what would happen later, when he grows older? Well, with such potions available, I think that's not a problem either? XD