The plot is quite unique. i don’t usually read dark/savior stories, so i might not be able to give the recs ur looking for. but here’s some that i think have a similar vibe (no obligation to read them, since most listed here are quite heavy-themed)
Otogibanashi No Owarikata (light hearted w/ some dark elements; reason: MC also has a traumatic past)
Boy Meets Maria (TW: pedophilia; reason: healing from a traumatic past. it’s a masterpiece, but gosh i cried so much. don’t think i will ever reread it though)
The Ex-tra Hot Neighbor (Korean Manhwa; light-hearted angst; reason: character development while exploring what it means to love and be in a relationship)
Chou to Hana no Kankeisei (reason: also deals with a tattoo relating to a traumatic past; check TW urself since i forgot major plot points as it’s been ages. i do remember crying to this)
My Way With You (Korean BL; reason: healing from past trauma; deals with grief)
the mc and ml are both engineers or scientists...the ml has a tattoo on his back of a Phoenix and he has a troubled childhood his parent sold him thats how he got the tattoo and the mc wants to invent something so he can fly