I dunno… As much as I admit that I started with KLS myself, the heavy pseudo-incest elements in it would turn of some people (I have a small siscon interest, but this wouldn’t apply to everyone)
In my humble opinion, we’d have to know if your friend can speak and read Japanese. That is a slightly important factor. If he’s limited to only English… then it shifts to interest.
Would he play purely for the sex ? Then any yarugee title by GC would please him, though the shenanigans in Mick Me Honey are slgihtly hard to beat. Does he want a game where there are no chocies, but he can reolplay his favourite fantasy ? Then there’s Chain: The Lost Footprints.
Now, leaving those aside, if he wants a ‘dating sim’… give him True Love, or its weaker knock-off, ganguro Girl.
And as for story… if he wants to continue on the whole ‘fanatsy roleplay’ aspect, give him Critical Point. If he wants ‘an old game’… give him Tokimeki Check-in.
The best is for last. If he doesn’t mind siscon… then by all means, give him Kana. If he wants some mystical elements… give him Figures of Happiness, Yume Miru Kusuri Tsukihime (sicne it’s fansubbed). If he wants horror: Divi-dead. I’d also recommend Crescendo.