Gifting something like 10 Milk tea works also to get ~500 amity, since you can romance him.

499 Amity with Manmehan Nesser in Valencia

Very easy if you have these knowledge first.

1. The Shadow of Nouver
2. Magic Carpet and Sand Pot
3. Five Ways to Cross the Desert
4. Human Astrology

Very easy to do this by giving him 13 milk tea.

Gelişmiş konsantrasyon iksiri 15 adet size 646 dostluk kazandırır

Манхан Несер
1. Тень Нубера
2. Волшебный коврик и кувшин с песком
3. Пять способов пересечь пустыню
4. Астрология человека

One of the easiest NPC got it in one conversation with costume and elixir.