I'm not sure about a specific 'Harry is Tom's subivisse fanfiction' but you can try looking on fanfiction platforms like Archive of Our Own. There are usually a lot of works there, and you can filter by tags related to Harry and Tom to find something interesting.
One popular Harry is Tom's subivisse fanfiction is 'The Unlikely Bond'. It explores their relationship in a unique way, with great character development.
The best chapter pointer here is Chapter 3, "Madam, the eldest young master has been missing for over half a month". It opens with Qiao was still annoyed at the attitude of this unknown girl when she heard... and closes on Jiang Yan, forced into a marriage with someone he did not love, had....
A practical answer is Chapter 13, because it turns the idea into a concrete scene. The chapter opens with Sensing that something was off with Jiang Yan, Jiang Yan dismissed the..., adds pressure through He probably had a good guess who it was., and ends on How could this happen..." Lin Manru.
Look to Chapter 39 for the clearest answer. It begins with Qi Tianyu had been looking forward to watching Jiang Li's drama unfold., keeps building through But to his surprise, Wen Jiaojiao, who seemed to possess some strength,..., and lands on His original intention was just to make Jiang Li back.
Chapter 866, "Why don't you die in his place?!", is the clearest early answer because it turns Didn's situation into a concrete plot event. The chapter gives readers a real answer by opening on In Shuiyun Temple, Changqing silently watched everything happening in...
Chapter 791, "There's Actually a Suona?!", is the clearest early answer because it turns Chen Taifan's situation into a concrete plot event. The chapter turns that into something concrete by moving from The lights in the audience suddenly went out, and immediately, the...
Chapter 835, "Is this your way of handling things? So pathetic.", is the clearest early answer because it turns Mommy's situation into a concrete plot event.
Chapter 836, "It's been a long time since I last saw Jin Siyue", is the clearest early answer because it turns Zhao Lang's situation into a concrete plot event. The chapter gives readers a real answer by opening on You!" Rong Junsheng seemed to have heard the commotion over here and...
If you want the clearest chapter reference, go to Chapter 2. Early on, On the top floor of the Financial Building, a gathering of dark clouds...; later, the chapter leans on How dare Jiang Li hang up his phone?.
If you want the clearest chapter reference, go to Chapter 11. Early on, After a meeting, Shang Shaojing pinched the bridge of his nose, tired, and...; later, the chapter leans on How is it going with the Jiang Family?" The assistant looked troubled and....
Chapter 821, "She Is Qingyang!", is the clearest early answer because it turns Feng Shui's situation into a concrete plot event.