This is not an anime however you possibly can strive Vocaloid songs.

Soundless Voice – Len Kagamine

Proof of Life – Rin Kagamine

Kokoro – Rin Kagamine

Len Kagamine-Prisoner

Len and Rin-Servant of Evil

Luka Megurine-Bullet for a Prisoner

Final Evening, Good Evening

Valshe-Soundless Voice

Magnet – Hatsune Miku and Megurine Luka

Paper Airplane – Kagamine Rin

Prisoner – Kagamine Len

Kingdom Hearts:

Dearly Beloved

Roxas Theme

Ventus theme

Sora’s Sacrafice

Past the clauds – Sayuri’s melody

Code Geass – Tales

Tsubasa Chronicles – Hear our prayer

Full Metallic Alchemist – Brothers

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Welcome my dear !
Do you want listen a brand new SAD LOVE SONG ?