I don't think my list will be very different from the others here (I might forget someone).
Yang/Orlok - Piofiore no Banshou (Like water and wine)
Lucas Sullivan - Mistonia's Hope The Lost Delight
Alma/White Mask(Iku Watase) - BAD APPLE WARS
Yonaga Soushirou - Jack Jeanne (I didn't really like the game, but it was the route I enjoyed the most.)
Peter White/JuliusMonrey - Heart no Kuni no Alice (I have a history with Peter)
Vilio/Zafora/Paschalia - Radiant Tale (I really liked the characters here)
Haiji Takumi/Akase Kyouya/Banjou Tomose - Charade Maniacs (Sorry, this game has a lot of characters)
Ishikawa Goemon/Murakami Yona - Tengoku Struggle -strayside-
Shigemori Akira - Hiiro no Kakera 2 (Why it was never ported to Switch)
Est Rinaudo/Alvaro Garay - Wand of Fortune
Karakurenai - Hana Awase (Ahh, my fault and pleasure, I love him)
Kano Riichiro/Saionji Toranosuke - Clock Zero
Rain - Armen Noir
Ukyo/Shin - Amnesia
Koumei - Sangoku Rensenki
Asahina Yuusuke - Brothers Conflict
Asahina Tenma - Glass Heart Princess
Tougane Chiaki/Kisaragi Kyouya - Kin'iro no Corda 3
Ciaran Lowell - The Red Bell's Lament (It's a little sad that it's the last route in the game)
Sid Whiteknight/Enox Harvardaff - Heart Cage
It reminded me that I need to replay Hakuouki; I have very vague memories of it to pick a favorite of mine.