The moment I saw the title I thought of Black butler - manga and anime. It is obvious that robot from Eternal butler wears exactly same costume as Sebastian from Black butler. Also the whole idea of a bit morally gray supernatural personal assistant called butler who also works in not obviously main character's best interest is exactly the same. Actually Eternal Butler feels like a sci-fi AU fanfic of Black Butler.

Although the plot and the genre and universes are very different (futuristic sci-fi and fantasy), what I find very similar is the insane amount of philosophical references in dialogues. Although said via main characters it feels like a background narrative as they attempt to philosophise every step of the story which doesn't really come to any certain conclusion. Almost like an essay.

First movie that they shoot in Every you, Every me is same plot as Color Rush. Although the storyline differs, the universe of colour blind people who see colour when they meet their soul mate is exactly the same.

Both main couples are tall well buit rich reserved guy and a poor infantile small twink who behaves like a baby most of the time except for sex scenes. Twink shyes away from kisses and calls sex "bad things you want to do to me" which gives mighty pedo vibes.

In a course of dramatic events Female lead from small town ends up in a big city where she tries to reconcile with her long lost sister, falling into forced relationship with mafia Male Lead which of course turns into real love. Sister is a singer, male lead saves female lead every 5 minutes, lots of long angry stares which are supposed to be cool. Probable Stockholm syndrome? Otherwise any feelings by FL make no sense. Gets very boring after ML and FL acknowledge their love because there is no further story past "and they lived happily ever after".

In both series an arrogant, abusive and weird male lead of significant wealth, position and power is hideously treating a resourceful but childish female lead until she falls in love with him for no reason at all. All characters are nearing their 40s and are of course virgins and never had any prior romantic relationships. Really similar main couple dynamics.

Supernaturally long living characters wait for the reincarnation of their long lost love who sacrificed themselves to save them. Once found, they begin love-hate relationships with the reincarnation because it is a must to lift a curse. They will literally die from the curse if they don't. A lot of long stares and awkward moments. Both are BLs.

Century of love is about a girl reborn in male body, while Mr Queen is a man reborn in female one. Both of their love interests are oblivious about the situation and take time to establish a relationship although of course it's love from the first sight. Characters in both series have conflict about being attracted to the same sex. Despite a different plot otherwise, the gender identity and sexuality conflict is very similar, plus magic plot with a lot of clowning by secondary characters.

Both series explore the relationship between a gay and straight men, where gay character accepts their own sexuality and is willing to fall in love and form a wholesome relationship, while straight one has his doubts and internal conflict all the way through their relationship.
Both stories begin with straight character being clueless about gay man's sexuality and assumes that gay man should be very popular with women, since he is very good looking. Straight character is super unlucky with women.
Even after they clearly formed a very loving feelings towards each other and strated their relationship as a couple, straight character has troubles accepting the fact that he is with a gay man, of what people around think, and most of all the physicality of their relationship. Straight character avoids sex as much as possible, while gay character is very sexually active. Gay character is also very gentle and loving, while straight one is rough and rude, and offensive and many times unfair towards his partner and can't get past his internal conflict. Gay character is also very patient and super forgiving.

Innocent is a better made, more mature drama about violence and abuse, but main couple is a nice kind male lead and mentally unhealthy male lead who behaves like a toddler. Their relationship and physicality have a lot of similarities with Secret crush on you and leave equally unpleasant unsettling feeling.

Heartbeat is not a BL, but it has the same trope of vampire sleeping in a coffin for 100 years and vampires doing magic rituals to become human again. Also this retinue the main character has is even visually alike to that of Heartbeat main. Even the ridiculous haircut is similar.

Bl love story between the dentist and the patient. Very cute characters, a lot of shenanigans. Sweet tooth isn't even out yet, but it seems like a remake of My Tooth your love even judging by the trailer.