A little JS and CSS to clean up WillMollyWilly and add a couple of navigational buttons for a more pleasant reading experience.

willmollywilly-assist.user.js

// ==UserScript==
// @name WillMollyWilly Assist
// @author Chris Kempson (chriskempson.com)
// @version 1.0.0
// @match *://blogs.yahoo.co.jp/willmollywilly*
// @grant none
// ==/UserScript==

// Replaces ----... with <hr>, adds class to sentence numbers, adds class
// to separators (＊＊＊... and *...)

var el = document.getElementsByClassName('entryTd');

for (var i = 0; i < el.length; i++) {
    el[i].innerHTML = el[i].innerHTML.replace(/[-]{4,}/g, '<hr>');
    el[i].innerHTML = el[i].innerHTML.replace(/(\([0-9]*\))/g, '<div class="sentence-number">$1</div>');
    el[i].innerHTML = el[i].innerHTML.replace(/([＊]{2,})/g, '<div class="separator">$1</div>');
    el[i].innerHTML = el[i].innerHTML.replace(/([*]{1,})/g, '<div class="separator">$1</div>');
    
    // Remove last hr
    var hr = el[i].getElementsByTagName('hr');
    hr[hr.length - 1].remove();
}


// Add scroll to previous/next sentence/paragraph and navigate to the 
// previous/next pages by on screen buttons or keypresses

var currentHr = -1; // Start from -1 so we advance to 0 (first HR)
var hr = document.getElementById('mainContentsArea').getElementsByTagName('hr');

// Inject buttons 
document.body.insertAdjacentHTML('beforeend', '<div id="buttons"><div id="previous">Previous</div><div id="next">Next</div></div>');

var previousNextA = document.querySelectorAll('.forwardNext a');
var previousHref = previousNextA[0].href;
var nextHref = previousNextA[1].href;

function scrollToPrevious()
{
    currentHr--;

    // Scroll to the previous hr or move to the previous page
    if (typeof hr[currentHr] == 'object') {
        hr[currentHr].scrollIntoView({ behavior: 'smooth' });
    }
    else {
        window.location.href = previousHref;
    }
}

function scrollToNext()
{
    currentHr++;
    
    // Scroll to the next hr or move to the previous page
    if (typeof hr[currentHr] == 'object') {
        hr[currentHr].scrollIntoView({ behavior: 'smooth' });
    }
    else {
        window.location.href = nextHref;
    }
}

// Bind to buttons
document.getElementById('previous').onclick = function() 
{
    scrollToPrevious();
};

document.getElementById('next').onclick = function() 
{
    scrollToNext();
};

// Bind to keypress
function keydownHandler(event) 
{
    // When using Yomichan with 'Automatically hide results' enabled,
    // Yomichan's popups cause the main window to loose focus and these
    // keydown events can no longer function ;_;
    switch (event.key) {
        
        case 'ArrowLeft':
            scrollToPrevious();
            event.preventDefault();
        break;
        
        case 'ArrowRight':
            scrollToNext();
            event.preventDefault();
        break;
        
        case 'ArrowUp':
            scrollToPrevious();
            event.preventDefault();
        break;
        
        case 'ArrowDown':
            scrollToNext();
            event.preventDefault();
        break;
        
        case 'j':
            scrollToNext();
        break;
        
        case 'k':
            scrollToPrevious();
        break;
    }
    
}
document.addEventListener('keydown', keydownHandler, true);


// Try to keep scroll and currentHr in sync

window.onscroll = function(event)
{
    // for (var i = hr.length - 1; i > 0; i--) {
    for (var i = 0; i < hr.length; i++) {
        if (isScrolledIntoView(hr[i])) {
            currentHr = i;
            console.log(currentHr);
            return;
        }
    }
};

function isScrolledIntoView(elem)
{
    var docViewTop = $(window).scrollTop();
    var docViewBottom = docViewTop + $(window).height();

    var elemTop = $(elem).offset().top;
    var elemBottom = elemTop + $(elem).height();

    return ((elemBottom <= docViewBottom) && (elemTop >= docViewTop));
}


// Inject CSS

document.body.insertAdjacentHTML('beforeend', `
<style>
/* Font stying and spacing fixes */

.entry {
    font-family: sans-serif;
    line-height: 2.25em;    
}

.entryTd font[size="4"] {
    font-size: 1.25em;
}

rt {
    font-weight: bold;
    color: #A77534;
    font-size: 0.55em;
}

r {
    line-height: 2.5em;    
}

.separator,
.sentence-number {
    font-size: 0.75em;
    font-weight: bold;
    color: #A77534;
    text-align: right;
    margin: -2em 0 -2.5em 0;
}

.separator {
    text-align: center;
    margin-bottom: -3em;
}

/* Hide annoying Yahoo Search popup*/

#yjSearchPop {
    visibility: hidden;
}


/* Expand the main body and hide the side column */

#sideColumn {
    display: none;
}

#mainContentsArea .entry .entryBody p {
    word-break: normal !important;
}

#mainContentsArea .entry .entryTitle {
    width: 894px !important;
}

#mainContentsArea .entry {
    width: 898px !important;
}

#mainContentsArea .entryMetaInfo,
#mainContentsArea .entryBody {
    width: 868px !important;
}

table {
    width: 100% !important;
}


/* Style the hr the JS inserts */

hr {
    margin: 1.75em 0 0 0;
    border: none;
    background-color: #A77534;
    background-image: url("https://s.yimg.jp/i/jp/blog/p3/images/folder/boxset/159/dot_hor3.gif");
    height: 1px;
}


/* Style the next/previous buttons the JS inserts */

#buttons {
    position: fixed;
    bottom: 25px;
    right: 25px;
    font-family: sans-serif;
}

#next,
#previous {
    background: #A77534;
    color: #fff;
    padding: 10px 20px;
    margin-top: 1em;
}
</style>`);