Playing Watson, I Turn the Witch Detective into a Loser

It is a beautiful age, and a mad one. Li Cha transmigrates to another world where occultism and steam industry have developed side by side. It is a place teeming with cursed objects, superhumans, and fanatics worshipping evil gods... There's just one problem: he'll be beheaded in a few days. "Would you like to be my assistant?" A young detective calling herself Sherlock Holmes says this to Li Cha in his prison cell. [You faithfully recorded everything the detective did, though she took issue with your notes on how she slept. Your compatibility with "John Watson" has increased further.] "Would you like to become my accomplice, Mr. West?" A mastermind makes him an offer. [You stole that young lady's heart and fulfilled your duty as a phantom thief. Your compatibility with "Lupin III" has increased further.] "Come, wizard! Let's burn the fiends to ashes!" An inquisitor reaches out to him. [You bravely charged the fiends, delighting the inquisitor. Your compatibility with "Don Quixote" has increased further.] [You extracted the source essence and gained a deeper understanding of the world's truths. Your compatibility with "????" has increased further.] "I don't understand. Why does everyone say Sherlock Holmes is a loser in love?" "We're just detective and assistant." "Can't we just solve cases together?" So, as a certain detective's absolute possession, and with the stifling feelings that come with it, what exactly has taught Watson to love...?