Both dramas revolve around contract relationships between the leads, which during the process one of them falls in love with the other. The stories are a little different, yet the main focus is the contract between them

Contract marriages for personal reasons. The leads fall in love during the contract.
The vibes are a bit different, but both are mainly focused on the contractual relationship

The stories are somewhat different, yet they have contract relationships in which the leads fall in love with each other.

Both are really romantic dramas
Both have body swaps
Go princess go has time travel too, but the day of becoming you doesn't

The FL in both dramas is Liang Jie
Both dramas have body swaps ( one between the ML and FL, the other one FL with the real body owner)
Both are really romantic and have great chemistry

Please come back Mister has body possession by two old ajussis who are reincarnated. They act weird and it's really fun to see them, yet The day of becoming You has no reincarnation but they swap bodies.

The only similarity between these two is the body swap
The stories are totally different and have different genres

Both dramas have Body Swap
The stories somewhat turn out to be funny for both leads
Big depicts the teenage side of being a different person, But the day of becoming you both are adults

The stories both revolve around fighting for justice
There is Amnesia in Both
similarly, the background stories are really elaborate and keep you entertained

Both are romantic fantasy dramas.
There are 3 stages: 1- first encounter in heavens 2- mortal realm and hardships 3-a massive war
The leads are really different. One is reserved, yet the FL is so bubbly and happy.
There is death and amnesia in both.
The leads fall in love deeply, but are separated due to misunderstandings and wars.
There is magic, devils, hatred, love, anything you wish for!
Both are the best in the era

Both are romantic fantasy dramas.
There are body swaps in each of them( Albeit a bit different)
One of the leads is Quirky and hates the other one at first.
There is Amnesia in both.
Lots of battles and gods and demons in both of them.
Love between fairy and devil is much more elaborate and has different stories included, yet The eternal love is quite simple.
Romance is so good in both

The leads are really similar. They go through so many hardships to find their genuine love
There are gods and battles, reincarnations, evils, fairies, magic, everything you desire for!
Each clan has their stories depicted quite interestingly.
The romance is just marvelous in both( You will love them from the beginning :)
Both dramas show Amnesia as a major substory
There are different stages included: From immortals and gods, to demons, and mortal world. Even the mortal hardships and punishments give off the same vibes.