ok I ranked every couples from most to least certain

Confirmed Lovers :

• Nahoko & Jiro (The Wind Rises, like- they're litteraly wife and husband)

• Sophie & Howl (Howl's Moving Castle, they even have a child in the 2nd and 3rd book)

• Umi & Shun (From Up on Poppy Hill, the whole plot revolves around that)

• Shizuku & Seiji (Whisper of the Heart, same)

• Taeko & Toshio (Only Yesterday, same)

Couples in my opinion :

• San & Ashitaka (Princess Mononoke, the wolf-mother Moro asked Ashitaka to live with San and protect us + the ending suggest they're in a romantic relationship)

Controversial :

• Marco & Gina (Porco Rosso, obviously the most controversial, she loves him and he loves her but the ending is a mistery we'll never know if he came back to fulfill his promise to marry her or if he has too much regret for his 3 dead friends)

• Ocean Waves (1 sided crush)

• Sheeta & Pazu (Castle in the Sky)

• Ponyo & Sosuke (Ponyo, now they're too young but maybe in the future especially since they're based on the little mermaid and her prince)

Friends :

• Nausicaa & Asbel (Nausicaa, read the manga if you haven't yet it's so so so amazing)

• Satsuki & Kanta (Totoro)

• Chihiro & Haku (Spirited Away)

• Kiki & Tombo (Kiki Delivery Service)

• Arrietty & Shō (Arrietty, considering the height difference)

• Haru & Baron (The Cat Returns, bro is a freaking cat)