To develop Professor Layton, you can focus on his intellectual side more. Show how he analyzes every situation and how his vast knowledge helps him make decisions. For Luke, you can show his growth. Maybe at the start he's a bit timid in solving really difficult puzzles, but as the story progresses, he becomes more confident. For example, you can have a scene where Luke is the one who figures out a crucial puzzle all by himself.
For Professor Layton, you could explore his past a bit. Maybe there was a particular event in his childhood that made him so interested in puzzles and mysteries. Reveal this through flashbacks during the fanfic. For Luke, develop his relationship with other characters in the story. Let him interact with people from different backgrounds and show how he adapts. He could also learn new skills from these interactions, like a new way of looking at puzzles. Also, show his emotional side more, like his fear when in a dangerous situation and how he overcomes it.
In a Professor Layton x Luke fanfic, to develop Professor Layton, you can give him some weaknesses. Maybe he's not so good at physical tasks. This can create interesting situations where Luke has to step in to help. For Luke, you can show his curiosity evolving. At first, he might be just following Professor Layton out of admiration, but later he starts to have his own questions and quests. You can also develop their relationship by having them argue about the best way to solve a problem. This shows their different perspectives and how they can learn from each other.
Chapter 156, "Mirror Immortal, 10 Days to Gather Beast Blood", is the clearest early answer because it turns Yuwen Hu's situation into a concrete plot event. The setup is Do you think the leader's decision was meant to exclude us?" "What..., but the pressure keeps building through He too lowered his head in thought, and soon, his expression subtly....
Chapter 168, "Snow Bamboo, Longyou, Sudden Wealth - Part 3", is the clearest early answer because it turns Arrow Bamboo Forest's situation into a concrete plot event. It opens with Xia Hong encompassed the entire Arrow Bamboo Forest on the scroll,... and closes on So far, Great Xia has ventured only about three to four kilometers.... The key payoff is that the chapter closes with Xia Hong paid it no mind at all;
Chapter 162, "Once and For All, Victory", is the clearest early answer because it turns Great Xia Camp's situation into a concrete plot event. The setup is The remaining forty-plus Earth-digging Realm individuals continued to..., but the pressure keeps building through On the other side, Gao Yu had long since been forced to the south....
Chapter 236, "White Dew Gu, Despairing Yuwen Dao, Yang Lu", is the clearest early answer because it turns Wu Ming's situation into a concrete plot event. Early on, Divide into four teams, attack from four directions, don't let them.... By the end, Inside the wooden house, the corpses on the ground had all developed.... Inside the broader battle storyline, the chapter closes with "Run, run, run fast!, which gives power growth a stronger narrative position and pushes the power growth onward.
Chapter 170, "Camp Integration, Territory Rapid Expansion (Part 2)", is the clearest early answer because it turns Xia Hong's situation into a concrete plot event. It opens with As expected of a giant camp, the number of people in the Logging... and closes on The top leaders, He Yuanhun and Yuwen Hu, only needed to oversee the....
Chapter 170, "Camp Integration, Territory Rapid Expansion (Part 2)", is the clearest early answer because it turns Great Xia's situation into a concrete plot event. The chapter gives readers a real answer by opening on As expected of a giant camp, the number of people in the Logging... and ending on The top leaders, He Yuanhun and Yuwen Hu, only needed to oversee the....
Chapter 172, "The Competitions Ends, Surprises Galore", is the clearest early answer because it turns Hong Yu's situation into a concrete plot event. The chapter turns that into something concrete by moving from Who the hell is dragging me... to Isn't it amazing?" Now Yuwen Dao's eyes were not just curious but....
Chapter 162, "Once and For All, Victory", is the clearest early answer because it turns Xia Hong's situation into a concrete plot event. The setup is At this moment, Shi Ping extinguished the fire of the Iron Refining..., but the pressure keeps building through Only the four Intermediate Cold Beasts remained unmoved..
Chapter 259, "Tasks, Helplessness, Ongoing Screening (Part 2)", is the clearest early answer because it turns Xiang Liang's situation into a concrete plot event. The chapter gives readers a real answer by opening on Like him, there are twenty-eight other people who took on this task. and ending on Soon, a majestic and solemn massive main building appeared in....
Chapter 255, "Frenzied Fortune-Making, Dangerous Thoughts, Perfect Timing", is the clearest early answer because it turns Xia Hong's situation into a concrete plot event. The chapter gives readers a real answer by opening on 60 drops of Cold Apple Jade Dew, 180 stalks of White Frost Grass, 180... and ending on Just this volume, the weight of a piece of silverware must far exceed....